Histria. Scanarea laser 3D a Turnului I / Histria. 3D Laser scanning of the Tower I

Abstract

The laser 3D scanning process was accomplished using a Leica ScanStation 2 device with the following main technical features : pulsed laser, 1 inch compensated double shaft, scanned pixel density < 1 mm, max. 50.000 pts/ sec. The area of interest was Tower I of the post-Gothic, Late Roman precinct at Histria. The equipment belongs to the Museum of National History and Archeology in Constanța and was professionally operated by Irina Sodoleanu and Laurenţiu Cliante. A number of Histrian monuments (Domus, the Episcopal Basilica, fragments of the Late Roman fortification) were scanned on this occasion, but only the results of the operation on the Tower I of the Late Roman, post-Gothic city wall, are presented. Tower I is part of the first monument that was excavated after the discovery of the city of Histria – the Late Roman city wall whose first phase dates back to the second half of the 3rd century AD. On the west front of the Late Roman fortification, Tower I occupies an important place because it was the corner tower during the first phase of this defensive work. In fact, it would continue to be the corner tower until the C-phase of the enclosure, which would expand south, including the new south-eastern city district – built on the land gained from the sea, due to the accelerated sedimentation process that was taking place during those centuries and created the rapidly advancing Saele sandbank. Moreover, Tower I has a very complex stratigraphic situation due to the place where it was built. It overlaps both the Hellenistic enclosure wall of the Acropolis and the first phase of the post-Gothic enclosure, as well as the constructive elements of the Thermae. At the same time, it is embedded in the later stages of existence of the Late Roman fortification. For these reasons, Tower I is difficult to investigate because parts of these structures are identifiable in its substructure, and others can only be observed and investigated in the interior space. It is worth mentioning the very special construction technique used to build this part of the fortification, which uses instead of a foundation, a layer of column bodies placed transversely to the direction of the wall. The Late Roman fortification was built as a result of the mid 3rd century AD events, which led to the decommissioning of the previous city wall, located about 400 m to the west and which had been constructed during Trajan’s reign. Because it could not be built further south, due to the presence of the sea water, it inevitably overlapped the previous defensive structures. That is why it used the Hellenistic Acropolis fortification as a foundation that provided the necessary solidity to a defensive structure, and the pragmatism of the Roman constructors could not ignore its presence. The Hellenistic Acropolis wall was overlapped in this corner by the first phase of the Late Roman fortification and by its corner tower, that is Tower I. In the monography dedicated to the Thermae, Alexandru Suceveanu made a fundamental observation : that the construction of this wall, which appeared under the southern side of the Tower I, does not use mortar and this excludes the possibility that it may be considered as the continuation of the northern wall of the Q room of the Thermae, which is the real post-Gothic fortification. Therefore, the relationship between this enclosure and the Thermae monument in its first stage is extremely important, not only for the configuration of the Thermal building, but also for the dating of this phase of the city wall. The explanation of what was considered to be an unusual situation, namely the construction of a city wall, after two centuries and a half, over another city wall, became evident in the meantime : the first phase of the post-Gothic fortification (called Phase A of the Late Roman city wall and dated to the reign of Emperor Probus) was built using the Hellenistic enclosure as the foundation because the latter had been built exactly on the natural boundary that separated the Acropolis from the sea during the period of operation of the Greek and Roman city enclosures. The pragmatism of the Roman builders has decided to use this structure, which had been still very well preserved, to build the new city limit – a limit that could not advance to the south due to the presence of the sea. Only phase B of the post-Gothic enclosure would expand 28 m to the south to settle on the marshland that became only recently usable for constructions. Excavations at the base of the western corner of the new corner tower (Tower K) have shown that the marsh land still required reinforcement of the soil works to build the new enclosure (Phase B of the Late Roman city wall) that now encompasses a whole new quarter. Although the research was particularly difficult due to the presence of the groundwater bedding that permanently covers the limestone tiles forming the foundation of the Hellenistic Acropolis enclosure, we had the chance to record them using the extremely precise 3D scanner.