By Neville Agnew

Some 2,400 years ago, Herodotus gazed in awe at the pyramids of Egypt, even then monuments of great antiquity. Besides being a historian, Herodotus was, in today's terms, the first cultural tourist and travel writer, and his accounts mirror our enduring interest in the past. As a window on the past—though often an obscured window—archaeological sites and ancient monuments allow us to look back in time to discern how cultures and civilizations lived, how they built, worshiped, and warred. This knowledge of the past enables us to place our own time in the frame of history.

While the rise of scientific archaeology—marked by 19th- and 20th-century excavations at Pompeii and Troy, for example, and the discovery of Tutankhamun's tomb in the 1920s—heightened public fascination with archaeological sites, this fascination has not led to great awareness of the risks to site survival. As with our natural resources, the archaeological store of sites is finite and nonrenewable, a diminishing resource increasingly under threat. Indeed, many threats to the natural environment and animal species imperil the cultural heritage as well. The 20th century has been witness to an explosive expansion in the global population, with attendant pressures on the archaeological record from industrialization, development, and various forms of exploitation, including an accelerated rate of legitimate excavation driven by scholarly pursuits. The marketplace, too, has created an illicit industry of looting sites for artifacts that eventually find their way into private and public collections. The tragedy of this activity is that looting sacrifices the site—and the vast amount of information that could be gleaned from methodical excavation—to the high market value of a relatively few objects. Lost sites, like extinct species, can never be regained.

A new and powerful factor has emerged in the latter half of the 20th century—mass tourism. In many developing countries, archaeological sites and monuments are a prime attraction for tourists. In purely practical terms, a natural alliance exists between tourism and conservation. Regrettably, in many countries the tourist dollar is funneled into central coffers, with only a pittance being meted out for site management and conservation. The temptation to maximize income from sites often leads to permitting more visitors than a site can safely accommodate. Consequently, physical attrition and vandalism inexorably degrade the monument or site. Similar threats have afflicted many natural and ecological parks, to the extent that in some countries it has become necessary to limit visitors.

The technical, scientific, and management requirements of site preservation are vastly more complex than are those for objects in museums. While museum collections are usually assured security and care within an environment where humidity, temperature, and light levels can be controlled, outdoor monuments and sites are exposed to destructive natural forces and often are not secure from looting and vandalism. Their preservation requires the input of many disciplines. A synthesis of the expertise of archaeologists, site managers, conservators, scientists, tourism planners, engineers, and geologists is necessary to formulate an overall preservation strategy that can be developed into a master plan for a site. The objective must be a holistic approach that can diagnose all threats and devise countermeasures, as well as a management blueprint with mechanisms to ensure implementation. A critical part of the planning process must be consideration of the views and needs of the local population.

Comprehensive site management has been an important emphasis in the Getty Conservation Institute's work, as has conservation for archaeologists. Both have been part of training courses, research, and field projects. The GCI has also conducted research and undertaken field projects related to specific issues such as adobe preservation (Fort Selden, New Mexico), site preservation and reburial (Chaco Canyon, New Mexico, and Laetoli, Tanzania), and conservation of sites in humid, tropical environments (Xunantunich, Belize). In addition, it has worked to facilitate the transfer of industrial and engineering techniques and materials to conservation purposes. The problems presented by mass tourism and the looting of sites have been addressed at length in a number of conferences and meetings coorganized by the Institute.

The future will bring yet more tourism pressures on sites, more looting for artifacts, and more destruction of sites. The listing by UNESCO of cultural sites and monuments of the highest value—the World Heritage Sites—has been an important step in raising public awareness, but the list is minuscule when compared with the world's vast number of sites. Future generations may well harshly judge this century—a time when species, both animal and plant, were exterminated, when forests were decimated, and the planet poisoned. All things connect, and so it is with our natural environment and cultural heritage. There is an urgent need to find ways to establish this link in the public mind and, through education, garner support to save for future generations the sites and monuments of humankind. They form part of the spectrum of what we value.

Neville Agnew
Associate Director, Programs

Conservation and Management of Rock Art Sites
by Nicholas Stanley Price

Rock art at Cueva Pintada in the mountains of Baja California Sur in Mexico. Photo: Guillermo Aldana.

Archaeological sites containing rock art—paintings or engravings—have increasingly come to be recognized as important sources of information for archaeologists, as well as places of fascination to the general public. However, until the Getty Conservation Institute identified it as a pressing need, there was nowhere in the world where the conservation of rock art could be systematically studied.

The GCI approached this problem by providing training opportunities at two different levels: a one-year professional program of full-time study, and short courses of one or two weeks that offered specialized knowledge of rock art conservation to those working in related fields. The one-year program was organized in 1989 with the University of Canberra in Australia as a Graduate Diploma course in the conservation of rock art. The 14 international graduates of the program subsequently took part in a month long field project organized by the GCI at the site of Painted Rock in California, where they completed the documentation and removal of extensive graffiti at the site.

The site of Painted Rock was also the locus, in 1987, of the first short, specialized course aimed at conservators. On the recommendation of one of the course instructors, the management of the site was recognized as a greater priority than treatment of its rock art. As a result, the general focus of the GCI's short courses on rock art conservation shifted toward site management. Three courses, in 1989, 1991, and 1992, were taught at the GCI on "Rock Art Site Protection and Management." (These courses led in turn to emphasis on management of archaeological sites in subsequent courses held in Cyprus and China, discussed elsewhere in this section).

The experience gained in teaching rock art conservation and site management contributed to the GCI Special Project on conservation of rock art in Baja California, Mexico, launched in 1994. Initiated out of concern for the outstanding rock art of the Sierra de San Francisco, the project was undertaken jointly with the Instituto Nacional de Antropología e Historia of Mexico, the Governor of Baja California Sur, and the Fundación Amigos de Sudcalifornia. Project tasks include documenting and analyzing the paintings' deterioration, implementing a management plan for the area's rock art sites, and training four professionals from Latin America in rock art conservation.

After less than 10 years' activity in this field, the GCI has trained 14 rock art conservators (the only professionals with diplomas in the subject); oriented over 60 archaeologists from the United States and abroad to the principles of site management; and established a new approach to the conservation and management of rock art sites in Mexico through its joint project in Baja California. The Institute has also, through analytical research by its Scientific Program, provided the first identification of the rock art pigments used by California's Chumash Indians. Together with the data on rock art techniques and materials forthcoming from the Baja California project, this information will make a substantial contribution to an area in which little systematic work has yet been done.

Nicholas Stanley Price
Former Training Program Deputy Director

Archaeological Conservation and Site Management
by Marta de la Torre

Participants in the GCI's 1992 management of grotto sites training course at the Yungang Grottoes in Datong, China.Photo: Margaret Mac Lean.

As described in the opening essay of this section, our archaeological heritage faces increased risk of destruction from unchecked development, new infrastructure systems, excessive visitation, and inappropriate interventions that attempt to "preserve" sites for tourists. At the same time, archaeological excavations, both licit and illegal, bring to light large numbers of artifacts that eventually find their way to museums, storage facilities, or private collections. Wherever they are deposited, they need care and conservation. Unfortunately, the national authorities and museums who have the primary responsibility for this heritage frequently must work with inadequate resources.

If our archaeological heritage is to survive for future generations, all who can influence its survival—or destruction—must recognize their responsibilities. Seeking to convey this message, the GCI organizes courses, seminars, and conferences for conservators, archaeologists, architects, and government officials.

Conservators have the specific responsibility to preserve objects and sites, yet few have had opportunities for training in the care of archaeological materials. Even fewer people are trained in conservation of archaeological sites and structures. In practice, the responsibility for this heritage often falls on archaeologists, architects, or civil servants whose training does not prepare them for the conservation problems they encounter.

Among all the types of collections, archaeological ones have received the least care. These collections are often vast and comprise a complexity of materials—two factors that make their conservation difficult. They are often held in university museums or in excavation storage areas, where the emphasis is on the gathering of and research on the objects, with little attention being paid to their condition.

To meet the urgent need for specialists in archaeological conservation, the GCI's Training Program has offered workshops directed at archaeology professors and graduate students in the United States and abroad. These workshops focus on the benefits that can be achieved—in terms of conserved information and objects—if basic conservation principles are observed during excavation. One innovative course on "Conservation and the Archaeologist" was offered in collaboration with ucla's Institute of Archaeology in 1993. In recent years, the GCI has been working for the creation of a degree program in archaeological conservation at a U.S. university.

A number of courses on specialized topics for conservators already working with anthropological objects have also been offered. In courses such as "Consolidation of Ethnographic Painted Surfaces," "Conservation In Situ," and "Conservation of Artifacts Made from Plant Fibers" (and the publication that resulted from it), the GCI worked with specialists from all relevant disciplines in order to systematize the knowledge required to care for anthropological collections.

The same activities that have increased the number of archaeological collections around the world have exposed sites to excavation and visitation. The conservation of sites is much more challenging than the protection of objects in a museum. Furthermore, their survival often depends on policy decisions regarding economic development, zoning, and tourism—decisions that are almost always made with little or no regard for site conservation.

The GCI has taken a leadership role in advocating the conservation of sites through professional management. In its courses, conferences, and Special Projects, it advocates a systematic approach to site management that has conservation as its main objective. The approach recognizes that archaeological sites are valued by different groups—archaeologists, local inhabitants, visitors, and national authorities—for different reasons, and that these values need to be both understood and conserved through a planned process that considers immediate and long-term needs.

The GCI has also offered a number of courses on the conservation of specific materials found at sites, such as wall paintings and stone. The courses target professionals working in the field and aim to provide them with an enhanced understanding of the nature and processes of deterioration of specific materials and a methodology for mitigating deterioration.

The Institute continues to develop a critical mass of professionals and policy makers who are concerned with the conservation of our archaeological heritage. Through its activities, it hopes to provide knowledge and tools that will strengthen efforts to preserve the past.

Marta de la Torre
Training Program Director

Adobe Preservation
by Neville Agnew and Charles Selwitz

Adobe ruins of Fort Selden, New Mexico, where the GCI is conducting research on adobe preservation. Photo: Neville Agnew.

And Pharaoh commanded the taskmasters of the people saying, "Ye shall no more give the people straw to make brick, as heretofore: let them go and gather straw for themselves. And the tally of the bricks, which they did make heretofore, ye shall lay upon them" (Exodus 5:6-8). Today the remains of these structures built of mud and straw brick still can be seen in Egypt.

Earth is among the oldest of humanity's building materials. For tens of centuries, people have combined sand and clay with straw and formed sun-dried bricks, known as adobe in the United States. Even today a significant proportion of the world's population constructs with earth, in many guises and with different techniques. While some countries have encouraged expensive and inappropriate modern materials to the detriment of traditional architectural designs, there is also a resurgence in the use of earth—in many areas its merits as a no-cost or low-cost material for dwellings have been realized anew.

Adobe preservation is among the most intractable of conservation problems. Under the impact of the weather, rain, and rising damp, adobe reverts to mud and slumps inexorably back into the earth. Traditionally, inhabited earthen houses and buildings undergo annual repair and maintenance, often with the introduction of natural additives in the mud for greater durability. With earthen archaeological sites, however, the objective is to save as much of the original material as possible, and regular maintenance by annual repair work becomes less acceptable because of attrition of authenticity over time.

The GCI became interested in researching adobe preservation in the late 1980s, after excavations at Tel Dan in Israel uncovered a triple-arched gateway of mud brick dating to the middle Bronze Age. Within a short time of exposure to the weather, it began to deteriorate rapidly, and the GCI was approached for help.

The Institute began its research in the laboratory, screening chemical consolidants that might enhance the resistance to erosion by water while retaining the appearance of the material and its ability to "breathe" (to transmit moisture without weakening). Promising results led in 1988 to a collaborative project at historic Fort Selden in New Mexico, where the Museum of New Mexico State Monuments was already conducting adobe research. Some 40 test walls were built and treated in a variety of ways, which included drainage, sheltering, techniques for repair of damaged adobe, and technology of reburial. Initial findings were presented and discussed at an international conference, "Adobe 90," coorganized by the GCI and organizations active in the field.

The best of the consolidants performed superbly, but high cost has mitigated against widespread use, so that cheaper alternatives have had to be found. Furthermore, when old adobe walls weather, the fabric becomes porous and extraordinarily fragile—chemicals, at the low concentrations used, cannot hold together this weathered outer skin, and the use of greater amounts of consolidant creates an artificial appearance. A new approach—a multistep process using three chemical procedures—has effectively stabilized sections of the adobe ruins adjacent to the test-wall area at Fort Selden. The walls were first strengthened by impregnation with a polysilicate; then a water-shedding crest of modified mud was built along the top of the wall. The entire structure was next covered with a thin veneer of modified mud sufficient to seal cracks. As a last step, the veneer was covered with a hydrophobic, or water-repellent, siloxane. The treated sections have gone through two winters without change.

Another blend of the procedures is being used to solve a different problem—replacing failed concrete or stucco coats on adobe walls with a more traditional adobe plaster. A durable replacement can be obtained, after the concrete is stripped, by stabilizing the walls with the polysilicate, plastering with amended mud, and spraying with a solution of siloxane.

Meanwhile, the Tel Dan Gate has been partly reburied and roofed by the Israel Antiquities Authority as preservation measures. The GCI is continuing its testing program and remains committed to conserving the important cultural resource of earthen architecture through related research, as well as training. A course on earthen architecture, planned by the GCI in collaboration with ICCROM and CRATerre, will be held in 1996 in Peru.

Neville Agnew
Associate Director, Programs
and
Charles Selwitz
Consultant, Scientific Program

The China Projects
by Neville Agnew

In January 1989 the GCI agreed to collaborate with the State Bureau of Cultural Relics (SBCR) of the People's Republic of China on aspects of conservation at two ancient Buddhist sites: the Mogao Grottoes, a World Heritage Site near Dunhuang City in the Gobi Desert in northwest China, and the Yungang Grottoes, near Datong, a coal-mining center some 320 kilometers west of Beijing. Interrupted by the events of Tianamen Square in June 1989, the projects were formally renewed in September 1990.

The ancient caravan routes linking China with the West—enduring from antiquity until about the 15th century—became known in modern times as the Silk Road. A great artery for the exchange of commerce and culture, the Silk Road in its heyday stretched from Xian (the ancient capital Chang'an) to Rome, a distance of 7,500 kilometers across the vast deserts of Central Asia. At the beginning of the first millennium, Buddhism traveled east from India along the trade routes, to take root in China. Dunhuang, an oasis town and gateway to China, was an important arrival and departure point. Here Buddhist monks dug hundreds of rock temples into a cliff face—the earliest in 366, the last around 1300. Nearly five hundred of these grotto temples remain, and lining their walls are paintings on clay plaster depicting legends, portraits, sutras, customs, costumes, and the arts. Some two thousand painted clay figures are also found within the grottoes.

After the gradual abandonment of the Silk Road, the caves remained a focus for local devotion. Following centuries during which the site declined, a Daoist priest named Wang Yuanlu began around 1900 restoring the cave temples and encouraging worshipers to visit. Wang also discovered the famous library in Cave 17, which had been sealed for centuries. Troves of ancient documents were removed by Western explorers early in the century and are now in museums in the West. Today the grottoes are under the authority of the Dunhuang Academy, founded in 1943. Its first director, Chang Shuhong, and his successor, Duan Wenjie, took the lead in documenting, researching, and publishing on the Mogao Grottoes. Since 1951, when the People's Republic of China officially established the Dunhuang Institute for Cultural Relics, the academy's staff has supervised conservation of the grottoes, directed archaeologists and artists working at the site, and guided the thousands of people who visit each year.

Working with the Dunhuang Academy, the GCI has addressed some of the major problems afflicting the site. Activities have included extensive windbreak fences to mitigate windblown sand sweeping over the cliff face, environmental monitoring within the grottoes, training in monitoring the color stability of the wall paintings' pigments, monitoring the structural stability of the cliff face, data analysis, and developing various engineering and management strategies. In 1993 the Institute, with the Dunhuang Academy and the Chinese National Institute of Cultural Property (part of the SBCR), organized at Mogao the conference "Conservation of Ancient Sites on the Silk Road," bringing together specialists from the West and East—in the ancient tradition of the Silk Road—to discuss common problems.

At Yungang there are over 50 rock-carved temples dating from 460 to 524, cut into a thousand-meter-long sandstone cliff face. Some 52,000 representations of the Buddha are carved directly in the rock, ranging from miniature bas-reliefs to statues 19 meters high. Many were restored in the Ming dynasty when mud plaster was applied over the eroded carving; the plaster was then elaborately decorated with polychrome and gilding.

The entire gamut of rock deterioration can be seen at Yungang. Damage is caused by several factors, including groundwater carrying soluble salts; rock fractures; physical weathering; pollution from nearby Datong; and dust, smoke, and particulate deposition on sculpture. Stabilization and rock pinning have been extensively undertaken by the Chinese authorities. Polychromy generally shows widespread loss of adhesion and cohesion. Deterioration of the surviving polychromy is due to crystallization of salt leached from rock by migrating water, wind and water erosion, pollution, inappropriate conservation procedures, and, historically, theft. Most external carving has disappeared as a result of weathering, and many statues were removed at the beginning of this century. The GCI and Yungang staff have done extensive testing to mitigate moisture infiltration and to implement environmental and pollution monitoring, scientific analysis of polychromy and pigments, and a formal training course in site management.

Following a joint evaluation of the collaboration by Chinese and Western specialists external to the project, the SBCR and the GCI agreed in 1995 that their collaboration will enter a new phase in the coming year.

Neville Agnew
Associate Director, Programs

The Laetoli Trackway
by Neville Agnew and Martha Demas

Martha Demas and Neville Agnew of the GCI examining details of the surface of the reexcavated Laetoli trackway during the 1995 campaign.Photo: Angelyn Bass.

Within the Ngorongoro Conservation Area of northwestern Tanzania lie Olduvai and Laetoli, two sites of great significance in science's attempts to unravel the maze that is the evolution of humankind. Olduvai is famed for its fossil bones of early man, while Laetoli is known for its tracks and traces of animals, including a trail of hominid footprints well preserved in volcanic ash now turned to soft stone. Each site has yielded parts of the mosaic of knowledge about the rise of humankind, but none more startling and intensely human than that of the Laetoli trackway—a short stretch of prints leading almost due north, as though symbolic of the early migrations to people the world.

Badly eroded in parts through natural processes where the overlying soil was thinned, the trackway was excavated in 1978 and 1979 by Mary Leakey to reveal a sequence of well-preserved footprints. After study and recording, they were reburied as a preservation measure. Trees subsequently grew in the reburial fill, and, at the Tanzanian government's request, a collaborative effort with the GCI was mounted to reexcavate, remove tree roots, conserve in situ, record, and study anew the footprints before reburying them again in a manner that will inhibit root penetration.

After several years of preparation and study, as well as consultation with a prestigious international advisory committee, a joint Tanzanian-GCI team conducted a major nine-week field campaign in the summer of 1995. Comprising conservators, archaeologists, palaeoanthropologists, photogrammetrists, and a scientific photographer, the team reexcavated, conserved, documented, and then reburied the southern half of the trackway. In 1996, the remainder of the trackway will be similarly treated.

Reburial as a preservation measure is increasingly accepted as perhaps the only way of saving a remote site such as the Laetoli trackway that cannot or should not be moved or left exposed. Too often fragile surfaces disappear within a year or two when left exposed to the weather and the attentions of souvenir hunters and vandals. The Laetoli site will be preserved in this passive manner--with regular maintenance and monitoring after 1996 by the Tanzanian authorities—to ensure its survival as a scientific and cultural resource. While reburial will mean that the footprints will not be accessible to the public, the Institute is developing reproductions of the trackway for display at the Olduvai Museum and at the National Museum in Dar es Salaam. These will be based on casts of the footprints made by Mary Leakey's team in 1979. The museum exhibits will also include photographs and material explaining the significance of the tracks, their conservation, and the need for protection through reburial.

The Laetoli trackway has great scientific value in the information it has provided, settling a long debate over which was first in the evolution of our species—the development of the brain or bipedalism. The prints, 3.6 million years old, precede by nearly one million years the earliest known stone tools and are therefore evidence that walking on two feet came first.

Their cultural symbolic value is no less profound. These footprints of our distant ancestors—so like our own—are the earliest traces of our long evolutionary journey. Africa, as the womb of humankind, fits the ancient adage today as well as two thousand years ago, when Pliny quoted a Greek proverb: "Out of Africa there is always something new."

Neville Agnew
Associate Director, Programs
and
Martha Demas
Conservation Specialist, Special Projects

Environmental Monitoring Stations
by Shin Maekawa

Shin Maekawa of the GCI assembling an environmental monitoring station inside the tomb of Queen Nefertari, Egypt. Photo: Neville Agnew.

When a field project is begun at a historic site, determining the surrounding environmental conditions is essential for an understanding of the forces of deterioration that may be at work. For conservators and site managers, that information assists in the development of an effective site conservation plan. Unfortunately, for most historic sites, environmental data are seldom available. Typically, there is not even a climatic monitoring station in the area.

In 1990, by adapting existing technologies in areas of environmental science, agricultural science, and industrial engineering, the Institute developed an environmental monitoring system to collect data pertinent to the conservation of historically important sites. It assists in comprehensive analysis of possible causes of site deterioration by gathering data on a site's climate, microclimate, and subterranean conditions, as well as on environmental conditions created by human activity. The system utilizes state-of-the-art electronic sensors, datalogger, and data communication for high-capacity, remote, and autonomous monitoring at the site. As such, it represents an important advance over the kind of handheld monitoring devices previously used by conservators.

The low-maintenance monitoring station is powered by a solar panel connected to a rechargeable battery and can be configured according to the requirements of a particular conservation project. Sensors to measure wind speed, wind direction, intensity of solar radiation, air temperature, relative humidity, and precipitation are standard in the system. In addition, the system can provide information on the presence of carbon dioxide, oxygen, and soil moisture, as well as record other conditions, such as surface and subsurface temperatures, dew condensation, and structural stress. All or some of the sensors are activated at a preset interval, and the processed data are recorded in the system over a programmed period. The system operates automatically 24 hours a day for an extended period.

Recorded data are transferred from the monitoring station to a personal computer, which produces data diskettes for later analysis. In many projects, a base station is set up at the conservation laboratory or site manager's office, and local staff members are trained to maintain the system and analyze the data. Some monitoring stations are equipped with modems and phone lines to allow transfer of the data to the GCI.

The environmental monitoring stations have been installed at many historic sites where the GCI has conducted field conservation projects. These have included sites in Belize, Bolivia, China, the Czech Republic, Ecuador, Egypt, and the United States. The stations can also provide useful insight into environmental conditions by counting visitors in order to identify their effect on the microenvironment within buildings and subterranean structures, such as caves and tombs. This information allows managers of the sites to develop suitable visitor management plans.

Shin Maekawa
Head, Environmental Science, Scientific Program

Chaco Canyon
by Martha Demas

A view of Pueblo Bonito, the ruins of an Anasazi settlement in Chaco Canyon, New Mexico. Photo: Guillermo Aldana.

In northwestern New Mexico lie the monumental remains of a vanished culture. Over a thousand years ago in Chaco Canyon, the Native American Anasazi established a series of settlements that included elaborately irrigated fields, a vast system of roads, and hundreds of stonemasonry structures, built from carefully cut blocks of sandstone. Extensively excavated since the late 1800s, the magnificent archaeological ruins of this ancient community now form Chaco Culture National Historical Park, a UNESCO World Heritage Site managed by the U.S. National Park Service (NPS).

In their mostly exposed state, the structures at Chaco Canyon--dwelling and storage rooms, plazas, and kivas--are subject to continual natural deterioration. The most erosive factor is water. In winter, snow piles up on the tops and at the base of the walls. When it melts, the water percolates down from the top, freezing at night within the walls and causing the masonry to buckle. Snow melting on the ground leads to rising dampness that erodes the base of the walls. Torrential thunderstorms during summer months cause surface erosion of soil and loss of mortar in the masonry. And, as at so many archaeological sites around the world, the demands of increasing visitation and of continuous protection of the ruins far exceed existing resources.

In 1991, the NPS and the GCI began a project to test strategies for protecting architectural remains such as those at Chaco. The project was based on the use of backfilling as a protective measure that is flexible and easily reversible, one that reduces maintenance while permitting visitation and interpretation of the site.

Although backfilling has long been practiced as a means of preserving archaeological remains, its effectiveness has never been systematically studied. In order to document backfilling's benefits, the project team reexcavated parts of six rooms in Pueblo Bonito that had been originally excavated in the 1890s and 1920s and partially backfilled soon thereafter. During the reexcavation, the rooms' present condition was extensively documented, then compared with their condition as originally excavated. The results dramatically demonstrated backfilling's efficacy, revealing excellent preservation of materials and features in areas that were reburied, while long-exposed portions of the site displayed significant deterioration. At the same time, the reexcavation pointed to the need for a more systematic approach to backfilling that would consider such factors as the types of materials being buried (e.g., wood, plaster, etc.), the climate and hydrology of the area, and the use of specialized fills and materials to achieve the optimal burial environment.

The GCI-NPS team also developed experimental strategies to protect walls from snow melt and to confront the problems posed by partial backfilling. All such procedures utilized geodrains and/or geomembranes—products made of geosynthetic materials used extensively in civil engineering—designed to prevent water migration, limit capillary rise of moisture, drain off surface water, or provide protection from snow accumulation. These strategies have potential applicability to other archaeological sites.

Using the lessons learned from the backfilling and testing programs, the team implemented a backfilling procedure for partial reburial of the ruins at Chetro Ketl in Chaco Canyon. This is part of a parkwide program to use partial backfilling to reduce maintenance while fulfilling the park's mandate to present the site to the public.

Martha Demas
Conservation Specialist, Special Projects

Xunantunich
by Martha Demas

The east frieze located at the top of the "Castillo," the tallest structure at the Maya site of Xunantunich in Belize. Photo: T. Torres. Courtesy of the Xunantunich Archaeology Project.

Buildings in humid tropical areas experience significantly different deterioration than structures in colder, drier, and more temperate regions. Lichens, fungi, and mosses on the almost continuously damp surfaces of exposed structures penetrate stone and loosen grains, thereby decreasing the stone's cohesive strength. High relative humidity and frequent rainfall gradually break down the soluble components in building materials. At the macro level, the intrusion of roots from lush tropical vegetation causes structural damage to abandoned buildings—especially archaeological ruins.

In 1992 the Getty Conservation Institute began collaborating with archaeologists from the University of California, Los Angeles (UCLA), and the Department of Archaeology in Belize to address some of the problems of conserving archaeological sites in humid tropical environments. The site of Xunantunich, an ancient Maya city inhabited between 700 and 1100 C.E., was chosen as the venue for project activities because it offered a rare opportunity to integrate conservation with excavation. Here, UCLA archaeologists are conducting a long-term research and excavation project that includes development of the site for tourism. The collaborative project has focused on three areas: scientific research and testing, architectural conservation, and training.

To better understand deterioration in humid tropical environments and to develop methods for conserving buildings, decorative stone, stucco, and mortar, the GCI developed a laboratory and field-testing program, now in its third year, researching the use of chemical consolidants for strengthening limestone and the use of biocides for controlling microflora growth. Solar-powered environmental monitoring stations were installed at the site to record weather data, which is being used to define test conditions for artificial aging tests in the laboratory.

Conservation of excavated structures disrupted by the intrusion of vegetation into the building fabric sometimes necessitates the dismantling and rebuilding of unstable walls and the addition of new materials. All too frequently, such interventions have led to total reconstruction and an inaccurate interpretation of the original structure's appearance.

At Xunantunich, current excavation is exposing several pyramidal structures in the central plaza. Archaeologists and conservators have together established a plan for the pyramids' conservation that would address a number of conflicting needs and values: the need to stabilize the structure and prevent further deterioration; the scientific value of retaining original materials; and the educational value of providing visitors with enough visual information to understand the structure. A three-year, on-site training program for technicians from the Belize Department of Archaeology in the principles and methods of architectural conservation took place both at Xunantunich and at the site of Copán in Honduras. In addition, the remains of a stucco frieze that originally surrounded all four sides of the largest pyramidal structure have been studied and conserved by specialists from Mexico's Instituto Nacional de Antropología e Historia, who also provided training for local technicians in the preservation of the frieze.

A key element of the project is conservation training. The GCI has organized seminars and workshops in Belize on management of archaeological sites and collections. An important initiative has been the development of a management plan for Xunantunich involving all parties with an interest in the site's preservation. The participatory process used for Xunantunich is intended to serve as a model for the development of similar plans for archaeological sites throughout Belize.

Martha Demas
Conservation Specialist, Special Projects