Construction and Building Technology in Sanctuary of Roman Settlement Aquae Iasae with the Review of Conservation Works on the Site

During the Roman period, the area of Varaždinske Toplice (northwestern Croatia) was the site of the Aquae Iasae settlement, famous for the healing properties of its thermal sulphur water. Around the thermal spring, the Romans built the sanctuary and to its south, a bath complex. The excavations conducted from 2011 to 2015 have shown that in the 2^nd century AD a rectangular structure of 8 × 13.5 meters in size was built around the natural hot spring i.e. a reservoir used for catchment, in the same manner as in the Roman settlement of Aquae Sulis (Bath). In order to make the ground suitable for construction oak piles were driven in below the walls before the foundations were laid down, while the terrain was stabilized in and around the reservoir. The walls of the reservoir – “sacred spring”, were built of large stone slabs, employing the opus quadratum technique. The walls were repaired in the 4^th century AD using older inscriptions, reliefs, and even sculptures as regular construction material (more than 50 stone monuments were found). The spring itself contained more than 17,000 Roman coins left as votive offerings. Most of the finds were in a very bad condition because of the detrimental effects of sulphur water, which calls for rather complex conservation approach.