Cabyle is one of the most important ancient cities in Southern Bulgaria with almost uninterrupted habitation for over a millennium between 4th c. BC and 6th c. AD. Philipp II found it as a Hellenistic town and it was later overbuilt by the biggest Early Roman castrum in Upper Thrace and a later castellum with Episcopal seat, while occasionally devastated by invading Celts, Goths and Avars. Disentangling the details of such dramatic history among the multilayered remains of one of the biggest archaeological sites in Bulgaria is a complex challenge calling for complex solutions.
The integration of various remote sensing and geophysical methods at different scale showed the high potential of their complementary use, as well as considerable heuristic value under challenging stratigraphic conditions. The following basic survey methods were applied: satellite imagery; imagery from airborne platforms - airplane and unmanned aerial vehicle (UAV), magnetic gradiometry, ground penetrating radar (GPR), electrical resistivity tomography (ERT) and kappametry. The combination of the chosen techniques provided huge amount of data. Their analysis and interpretation served to solve different tasks related to spatial analysis of ancient city of Cabyle and its surroundings, 3D modelling of the terrain and the ruins of several buildings, directing future archaeological excavation works, searching for new targets and locating completely unknown structures buried under ground, etc.
The use of car-towed 16-probe magnetic gradiometer array was instrumental for quick and detailed mapping of extensive areas and turning the focus on prospective locations within the city limits, while also unexpectedly revealing a new bath complex beyond the city walls. ERT helped to map the thickness of the anthropogenic layer, the depth to the fundament rocks and to distinguish geological faults from massive walls. The GPR was most successful in outlining the plan of an important part of the Roman town hidden underground, whereas aerial photography indicated part of massive building with East-West orientation indicated by significant differences in the color of the crops.
Archaeological excavations informed by the survey results demonstrated a very close match between the linear features visible both on the vertical gradient map and on the GPR model on one hand and the excavated architectural remains on the other. This case study may serve as a perfect illustration of the usefulness of integrated application of remote sensing methods for informing strategic decision-making and long-term management plans of archaeological parks and monuments.