November 2025: The harbours of Roman Osor

As part of the project, the topographical location of Osor was examined in detail (Miko et al. 2025). The town’s location next to the Osor Channel has given rise to many myths about Osor. These include questions such as whether Osor was ever an island and how many harbours it had. While the belief that Osor was an island in the past was disproven in 2019 (Draganits et al. 2019), the new research has focused on verifying the prevailing interpretation that the northern Roman port was in Bijar Bay and the southern one was in Jaz Bay, to the south of Osor.

Although Jaz Bay appears to be a natural harbour, it is actually the result of a combination of natural sea level rise and human intervention. Two drill cores were taken from the bay, one of which was dated using optically stimulated luminescence profiling and dating (OSL-PD) method. This method provided a date range of 170±100 AD for the flooding of what is now Jaz Bay. This suggests that Jaz was dry land until the early Roman period, developing into a marsh due to rising sea levels over the centuries. This leaves Bijar Bay as the only possible location for the Roman harbour.

The Jaz Bay during the archaeological and geological surveys, and the locations of the core samples taken.

Documentation of the stone bollards in Bijar Bay. Simulation of a 1.5 metre lower sea level during Roman times using ALB data indicates that the bollards were actually situated above the Roman sea level (as shown by the dotted white line in the image below right). However, it is no longer possible to provide solid proof that they were carved in Roman times.

29. November 2025