Prospecting in Ostia Antica (Italy) and the Discovery of the Basilica of Constantinus I. in 1996

Abstract

Cooperation of Bavarian State Conservation Office. Department Archaeological Prospection and Aerial Archaeology (H. Becker). German Archaeological Institute Rome ( P. Zanker. M. Heinzelmann). Institute for Photogrametry and Remote Sensing Technical University Munich (M. Stephani. K. Eder. R. Brandt). Bayerische Akademie der Wissenschaften (Kommission zur Erforschung des antiken Stadtewesens) Munchen, Soprintendenza Archaeologica di Ostia (A. Galina Zevi). After the huge excavations in 1938 to 1942 in Ostia Antica. the ancient habour of Rome for the World Exhibition 1942 in Rome, there remained about 40 hectare of the area of the ancient city untouched. This is about 50 to 60% of the original built up area. On one hand the untouched area would be a chance for future research work in Ostia. at the other hand this was always a handicap for urbanistic research. The ideas about the building structure in some quarters of the city (regiones) as well as about the distribution and type of various buildings will be almost hypothetical. Even the location of some important buildings like the amphitheatre and the temple of Volcano are still unknown. Therefore the department Rome of the German Archaeological Institute began to organize a experimental project testing modern methods for archaeological prospecting for urbanistic research. The combination of aerial photo interpretation of several sources, digital terrain modelling and geophysical prospecting (caesium magnetometry and resistivity surveying) were applied on the base of the same coordinate system. An area of about 15 ha. the biggest untouched area, in regio V in the southeast of the ancient city was selected for a first test for geophysical prospecting in August 1996. The limits of this test area were chosen very close to the excavated parts of this regio. to the south and east it was spread far beyond the ancient city wall reaching the modern fence of the archaeological area. Hopefully in this area used as ploughed field for agriculture the archaeological structures should remained untouched and buried not very deeply. Considering the time of ten days only for this first test in August 1996 caesium magnetometry was applied only, because resistivity surveying seemed to slow for vast areas. The summer in 1996 was also very dry with temperatures sometimes above 36° Celsius (in the non-existing shadow), which would have caused severe electrical contact problems to the ground. After a very limited test for resistivity surveying in area where the basilica was found in 1997 there was a bigger area surveyed by resistivity methods in June 1998. which gave almost no additional information about the archaeology in the ground that could be seen already in the magnetograms. This was also the first test for a quadro-sensor caesium magnetometer system mounted on a non magnetic chariot ( the socalled "Magneto-Scanner"(Fig. 1). This new system consists of 4 caesium magnetometers Scintrex SMARTMAG SM4G-Special with quadro-sensor configuration. 2 gradiometcr consoles, data loggers, power supply (4 batteries 12V/6Ah). interface electronics and automatic distance trigger mounted on a nonmagnetic chariot, total weight about 50 kg. A fifth magnetometer can be used for compensating the daily magnetic variation synchronised in a variometer mode. The whole system (5 magnetometers and the chariot) can be packed into any normal personal car (there is no van necessary). The "Magneto-Scanner" had to be built up rather quickly to be ready for the test in Ostia within some weeks. Several persons and companies helped for this fast construction: The main part of this system was sponsered by the Bayerische Motorenwerke AG BMW. the nonmagnetic chariot was built by my brother Dr. Thomas Becker the construction was made during manufacturing and Scintrex (Canada) succeeded in fast delivery even for the modified sensor-systems SM4G-Special. Jorg Fassbinder helped solving many problems due to the interface electronics and the distance triggering and Rainer Appel succeeded finishing a software