Multidisciplinary Research at the Cave of Letters, Israel: A Melding of Physical and Social Sciences

Philip Reeder, Department of Geography, University of South Florida
Harry Jol, Department of Geography, University of Wisconsin-Eau Claire
Paul Bauman, Komex International, Inc.
Richard Freund, Maurice Greenberg Center for Judiac Studies, University of Hartford

1. Introduction

Research in 1960-61 by famed Israeli archaeologist Yigael Yadin, in what came to be called the Cave of the Letters (COL), yielded a priceless collection of artifacts including scrolls, pottery, coins and bronze objects. Jewish rebel commanders, and their families, who sought refuge in the cave near the end of the Second Jewish Revolt against the Romans (~135 C.E.) left these objects. An archive of 70 documents in Hebrew, Aramaic, Nabatean and Greek were discovered in the cave. About a dozen letters bore the name of Simeon Ben Koseva, the historical figure known as Bar-Kokhba, leader of the Second Jewish revolt. The Bar-Kokhba letters were mostly military documents that contained plans and orders. Another cache of documents recovered from the cave was the personal archive of Babatha, a young woman from a remote village in the Dead Sea area. The bundle of documents she left chronicles what life was like for a Jewish family at this important time in history.
No research was conducted in the cave between 1961 and 1999, and it was postulated that a substantial amount of new information about this unique period in history remained to be discovered. Research expeditions to the Cave of Letters in July 1999 and July 2000 utilized state-of-the-art technology, as well as traditional geologic, archaeologic and surveying techniques, to add a substantial amount of new information to the existing bases of knowledge about the Second Jewish Revolt, as well as the viability of geophysical research in caves. Because the COL is located in the tectonically active Dead Sea Rift Zone (Figure 1), and local limestone layers are being wedged apart by the growth of gypsum crystals, the cave floor is covered with roof fall that obscures the underlying archaeological deposits. Ground Penetrating Radar (GPR) was used in the interpretation and reconstruction of living surfaces below the roof fall. Other geophysical analyses included the use of two-dimensional electrical resistivity tomography (ERT) to further image the rebel occupation surfaces, and a gradiometer and a high-resolution transient EM metal detector were used to locate artifacts in and below the rubble. The data necessary to produce new, detailed maps of the cave was also collected, and a series of new maps were created (two of which are presented in Figures 2 and 3).

2. Historical Background

In 132 C.E. the legendary Shimeon Bar Kokhba led the Second Revolt of the Jews against Roman rule. The First Revolt, which occurred 62 years earlier, ended with the famous resistance at Masada. During the Second Revolt, Bar Kokhba's troops captured Jerusalem, and restored the Jewish state, but they were eventually defeated in 135 C.E. by the Roman general Julius Severus. Events associated with the First Revolt, recorded by Josephus Flavius, are part of the historical record for this period. No such historian existed for the Second Revolt, so for nearly 2,000 years Shimeon Bar Kokhba remained a mythical figure known mostly through Jewish folklore. All of this changed in 1960 when an archaeological expedition headed by Yagael Yadin explored a cave in the Nahal Hever near the village of En Gedi (Aharoni and Rothenberg, 1960; Yadin, 1963).

During Yadin's excavations of 1960-61, Hall "A" yielded a large cache of bronze objects, as well as other assorted artifacts. Excavations in Hall "B" led to the discovery of a fragment of a scroll that contained a rendering of an old psalm. Then, in Hall "C" the expedition discovered a bundle of leather that later proved to be a goat waterskin. Contained inside this package were beads, perfume flasks, cosmetic tools, a hand mirror and a bundle of papyri tied with string. Among the papyri were four wooden slats that were covered with writing, which were later determined to be letters from Shimeon Bar Kokhba to military commanders stationed at En Gedi. The first wooden slat contained the heading "Shimeon Bar Kokhba President over Israel." The goatskin belonged to the wife of Yehonatan bar Be'ayan. When she fled to the cave she had taken it with her as part of her household belongings (Aharoni and Rothenberg, 1960; Yadin, 1963).

3. Methodology

In order to create a new, detailed set of maps for the Cave of Letters, a survey was completed using hand-held survey instruments that included 1) an optical compass, 2) an optical inclinometer and 3) a nylon survey tape. A total of 82 survey stations were established within the cave. Data collected between each station includes azimuth, inclination, and distance. At each survey station a sketch of that segment of cave passage was also produced. The survey data was plotted using the CAVEPLOT computer program, and the plots were exported to Adobe Illustrator for map production. Plan view and cross-sectional maps were produced, as well as maps that depict the locations where geophysical and archaeological analyses were completed (see Figures 2 and 3).

A portable digital pulseEKKO™ 100 and 1000 GPR system was used to obtain the GPR profiles. Four antennae frequencies, 100, 200, 225 and 450 MHz, were tested. To reduce data collection time in the rugged cave environment a backpack transport system was employed. The digital profiles were processed and plotted using pulseEKKO™ software. The application of radar stratigraphic analysis, an approach for interpreting sedimentary environments (Beres and Haeni, 1991; Jol and Smith, 1991), provided the framework to investigate both lateral and vertical geometry of the reflection patterns. After processing, printing and interpreting the GPR profiles while in the cave, archaeological probes were completed at selected locations using an endoscope, metal detector, and/or traditional archaeological excavation techniques.

The two-dimensional electrical resistivity and tomography (ERT) analysis involved introducing an electrical current into the cave floor with two electrodes, and measuring the voltage drop across the surface with two other electrodes. Because electrical flow disperses throughout the geologic materials that make up the floor of the COL, these measurements provided information about the electrical character of materials below the surface of the cave floor. Profiles were produced by modeling the data from a series of measurements with different depths and locations along a survey line (Reynolds, 1997). In the COL two electrical resistivity and tomography transect lines were established (Figures 3, 5 and 6). A gradiometer and a high-resolution transient EM metal detector were also used in the COL, with limited success, to locate artifacts in and below the rubble.

4. Results and Discussion

Very detailed maps of COL were prepared after the 1999 and 2000 expeditions. Using a base map created with Adobe Illustrator (Figure 2), additional maps were produced that included 1) a map that depicted the location of roof fall and the topography of the cave floor, 2) a cross-section of the cave, which also became part of many of the other new maps, and 3) detailed cross-sections from 22 different locations in the cave (lettered "a" through "v"). An archaeological finds map was produced after the 1999 and 2000 expeditions, and maps were also produced that depict the location of GPR or ERT survey lines. Figure 3 contains many of the map components discussed above. The maps created based upon this research are the most accurate maps ever produced of the Cave of Letters.

As part of the GPR analysis, a three-dimensional data set was collected from a 5.5 m by 2.5 m grid in Hall "B" (Figure 4). Three-dimensional datasets of this type greatly aid in interpreting the framework of the subsurface materials and provide a more detailed view of the geometry of individual units. This experimental data set enhanced our ability to interpret the three-dimensional geometry of the Bar-Kokhba floor, which appears within the cut out of Figure 4. The ERT and GPR data corroborated each other regarding the location of the Bar Kokhba living surface, and in some instances ERT more clearly delineated this surface. Figures 5 and 6 are cross-sections produced from the ERT data that clearly indicate not only the location of the Bar Kokhba surface, but the nature of the geologic materials found below the cave floor.

In Figures 5 and 6, based upon interpretation of the ERT data, the Bar Kokhba living surface has been differentiated. Also indicated are areas of recent rockfall, ancient rockfall, and bedrock. ERT and GPR analysis in the COL were used to indicate optimum zones for endoscope analysis and excavation.

5. Conclusions

This research marks the first successful use of GPR to delineate living surfaces buried in a cave environment. Both GPR and ERT indicated areas below the rubble for endoscopic viewing and archaeological probes. Based on cave surveying, a set of detailed maps were produced, and the length of the cave was determined to be 525 meter, which is 275 meters longer than previous surveys indicated. By utilizing a multidisciplinary approach, and working within the framework of the emerging field of geoarchaeology, unique insights were gained with respect to the use of geophysics in cave research, and that coupling traditional archaeological and geographical methodologies with geophysics can provide a new and unique understanding of the importance of the COL.

Key Words: geophysics, geoarchaeology, mapping, archaeological probes, cave

6. References

Aharoni, Y. and Trothenberg, B., 1960. In the Foosteps of Kings and Rebels in the Judean desert (Hebrew), Massada, Tel Aviv, 189 pp.

Beres, M., Jr. and Haeni, F.P., 1991. Application of Ground-Penetrating-Radar Methods in Hydrogeologic Studies, Groundwater, Vol. 29, pp. 375-386.

Jol, H.M. and Smith, D.G., 1991. Ground Penetrating Radar of Northern Lacustrine Deltas, Canadian Journal of Earth Sciences, Vol. 28, pp. 1939-1947.

Reynolds, J.M. (1997) An Introduction to Applied and Environmental Geophysics. Wiley, New York, 796 pp.

Yadin, Y., 1963. The Finds From the Bar Kokhba Period in the Cave of Letters. The Israel Exploration Society, Jerusalem, 279 pp.