UNDERWATER GEOPHYSICAL SURVEY OF THE SUBMERGED SETTLEMENT IN FRONT OF THE MOUTH OF THE RIVER OF ROPOTAMO (Lyudmil Vagalinski – lvagalin@techno-link.com, Kalin Dimitrov) Geophysical survey in the maritime aquatory in front of the mouth of the River of Ropotamo were carried out, in the gulf to the south of St. Demetrius Cape. The aim was to identify promising locations for the underwater archaeological excavations and preliminary information on the stratigraphy of the site to be collected. An area of 38 ha was explored with a multi-beam echo sounder. An area of c. 40 ha was scanned with lateral scanning sonar. Vertical electric underwater drilling was performed at 471 points with a depth of penetration into the sea bottom of 5 m to 25 m. Visualizations and 3D models were built to support the archaeological explorations. The positioning of the archeological trenches according to data from the geophysical surveys has led to successful subsequent archeological excavations. The ancient mouth of the River of Ropotamo was located at c. 700 – 800 m to the northwest of the present-day one. During the Early Bronze Age when the sea level was 8 – 10 m lower than today, the gulf between the mouth of the river and St. Demetrius Cape was a coastal terrace. A settlement existed on that terrace during the Early Bronze Age, situated on the banks of small right tributaries of the River of Ropotamo.