IDENTIFICATION OF STONE BLOCKS USED FOR THE BUILDING OF THE THYSDRUS AND THAPSUS AMPHITHEATRES IN TUNISIA

In Tunisia, the largest amphitheatre (known as the Coliseum) at Thysdrus (El Djem), with some parts of the second amphitheatre, and the Thapsus amphitheatre have been built with squared stone blocks (opus quadratum). The petrographic and geotechnical analyses of the samples taken from the amphitheatre blocks show that these blocks belong to the Tyrrhenian and to the Mio‐Pliocene age. Ancient quarries have been found on the Tyrrhenian dune line between Hiboun and Al Alya, at a distance of 30 km from Thysdrus, from which the Tyrrhenian blocks have been extracted. Concerning the Mio‐Pliocene blocks, they have most likely been cut from just one ancient quarry found in the hill of Ksour Essaf. The height of almost all of the measured blocks from the Thysdrus Coliseum is equal to the Punic cubit used at Carthage (50 cm), and the height of the measured blocks from the Thapsus amphitheatre is also equal to the Punic cubit (50 cm), or very close to the Roman cubit (45 cm).     

AN APPRAISAL OF THE PROBLEMS INVOLVED IN THREE-DIMENSIONAL GROUND PENETRATING RADAR IMAGING OF ARCHAEOLOGICAL FEATURES

There are a number of problems that are due to the physics involved in the ground penetrating radar (GPR) technique which result in the recorded data giving a distorted representation of the true subsurface structure. Many of these problems are reduced by the experience of the person interpreting the data. This paper is an attempt to remove some of the subjectivity from this process by considering how the distortion in the data could be reduced by applying a migration routine. The amount of data, and the time needed to collect it, place a restriction on the use of the migration process to two dimensions only and result in a compromise approach to the use of GPR. This compromise may, however, result in better integration of GPR with the other geophysical techniques available.     

AN ARCHAEOLOGICAL INTERPRETATION OF GEOTECHNICAL SOUNDINGS UNDER THE METROPOLITAN CATHEDRAL,MEXICO CITY

The Metropolitan Cathedral of Mexico City has undergone alarmingly large differential settlings. An extensive geotechnical investigation programme was performed in its subsoil, as part of the studies required in an ongoing salvage project. The results of many of the soundings performed can be interpreted from the viewpoint of the archaeologist. This paper shows, based upon the framework provided by previous archaeological research performed in the cathedral, that the geotechnical investigations allow the unique opportunity of establishing hypotheses regarding the extent and distribution of some of the structures that existed in the ritual precinct of Tenochtitlan, as well as of its foundation.