Altinum (Kölked). GPR surveys 2017–2020

Abstract

Our knowledge about the known Late Roman fort situated in a currently unbuilt area is based on various non-invasive surveys. Relying on the aerial imagery and the magnetometer-survey conducted in 2009, the extents of the fort and the structure of its vallum can be specified quite accurately. Due to their nature, the previous investigations could only clarify the position of the main wall and the towers of the fort, while they were unable to specify the possible building phases. We could presume how built-in the internal areas of the fort were, however, it has been impossible to reconstruct the plans of the inner buildings. The Ground-Penetrating Radar allows us to identify wall remains belonging to former, demolished construction periods. It makes it possible to obtain information about the plan in areas polluted by debris and larger metal objects. The surveyed 9245 sq. m surface is 52% of the currently accessible area (17750 sq. m), however, our targeted excavation trenches provided new data about the entire vallum. The systematic survey of the inner areas could provide new information. Based on the surveys, towers belonging to 3 main types (U-shaped, fan-shaped and larger, trapezoidal towers with one internal pillar in each) and an apsidal building have become known. The gate of the fort could not be located. It is possible to be found on the partially inaccessible north side, or on the east side, which was completely destroyed by erosion. The stratigraphic observations of the excavations conducted in 1975 and 2018 in the area of the fort helped refine the calculated depth data of the GPR measurements thus, hopefully, the relative depth data that we specified are approximately accurate. Our surveys indicated that the northern part of the hill is more destroyed, here our measurements could detect fewer features and to a smaller depth compared to the southern side. In some places – in the western part of the apsidal building or inside the large tower to the south – the existence of earlier construction phases can also be proved or assumed. The GPR measurements have also shown the trace of the via sagularis running parallel to the vallum. Hopefully the smaller and larger wall sections found at the edges of the survey areas will be interpretable with the future extension of the GPR surveys.