A joint project of the Deutsches Archäologisches Institut and the American Academy in Rome begun in 1996 to investigate the unexcavated areas of the city of Ostia is coming to a close after six years, which suggests drawing a preliminary balance. This experimental enterprise had the goal of investigating how field archaeology can make an up-to-date contribution to answering urbanistic questions. Up-to-date means taking into account the ever scarcer financial and personnel resources, limits of time and also the obligation to spare the original substance as much as possible. These conditions rule out a traditional extensive excavation, until now field archaeology's only methodological possibility in clarifying urbanistic questions over a large area.

The following procedure was developed as an alternative concept. In the first stage of the, between 1996 and 2001, almost all of the unexcavated areas of the city of Ostia were investigated by means of geophysical surveys. A then newly developed cesium magnetometer with a four-sensor array allowing particularly quick work was used throughout. In four seasons ca. 70 hectares of the city could be analyzed. Magnetometry proved to be extremely successful in many areas. Not only streets and large building complexes were discovered but on many occasions even single rooms. Electroresistivity was also employed in certain selected zones. Since this takes significantly more time and gave only slight additional information, it was decided not to apply it throughout.

Aerial photographs are another important source of information. All together about 30 pictures taken between 1911 and 1998 were found in various European archives. An aerial photograph of 1985 was particularly valuable because numerous archaeological structures could be recognized on it in great detail. After these images were transformed into digital orthophotos, they were combined with the results of the geophysical surveys in a geo-information system (ArcView) on the basis of the Italian surveying system and evaluated archaeologically. The combination of these sources of information allows the original plan to be reconstructed to a density of 40-80% according to the zone investigated. Furthermore, a digital model of the terrain was developed on the basis of the aerial photos, which together with the results described above can reveal potential preserved elevations of wallsn - or in the case of the newly confirmed river port basin - notable depressions in the terrain.

Although the systematic application of these non-destructive methods of investigation allow an great increase in our knowledge of the plan of Ostia, the data obtained lack any temporal dimension. Therefore, stratigraphic sondages were undertaken in a second phase of the project starting in 1998 in order to date single structures or to clarify long-term sequences of use (e.g. of streets) by means of the analysis of pottery and other finds. Because of the survey results available the sondages could be placed with extreme precision and carried out with the smallest possible surface area. Thus, the unavoidable destruction caused by archaeological operations could be kept to minimum. Since the sondages are backfilled, there is no obligation for long-term restoration. The sondages' relatively small surface areas keep the quantities of finds, which can easily become enormous at Ostia, within manageable proportions, while providing sufficiently large scale samples for reliable analyses. A new programmed inter-relational data-base allows a quicker documentation and a better access to all types of data (excavation data, photos, drawings, small-finds, ceramics etc.).

So far 37 sondages have been carried out in various parts of the Regions III, IV and V. The main points investigated were the newly discovered Constantinian basilica, the late republican city wall with two previously unknown gates, two large domus and a large villa suburbana in the outskirts of the city, various horrea and other utilitarian buildings of a commercial nature, numerous streets, a large river port basin with navalia and a temple within the mouth of the Tiber.

To summarize in a preliminary way, the application of geophysical survey methods over large areas, which has become possible in recent years, has proved to be an ideal complement to traditional aerial photography and opens completely new perspectives for general urbanistic research. With the rapid progress of technology even better results should be possible in the future, with remote sensing from satellites being potentially of particular importance. However, the results of these non-invasive methods are especially effective in answering urbanistic and historical questions when they are coordinated with stratigraphic investigations designed to clarify the temporal dimension. This combined methodological procedure offers an appropriate instrument urbanistic research to gather a great mass of new information with relatively short projects and limited means.