UNDERWATER ARCHAEOLOGICAL SURVEY IN THE SOUTHERN HARBOR OF MESAMBRIA (Nayden Prahov – naydenprahov@yahoo.com, Kalin Dimitrov) The area for the dredging works, which was explored, was c. 400 m long and c. 100 m wide. The harbor was from 6 m to 9 m deep. Diving surveys were carried out and geophysical explorations were performed with a multi-beam echo sounder and side-scan sonar, on the basis of which a detailed bathymetric 3D model was created. During dredging works in the past, a number of archaeological finds were discovered in the harbor.

UNDERWATER ARCHAEOLOGICAL OBSERVATIONS IN THE SOUTHERN HARBOR OF MESAMBRIA (Nayden Prahov – naydenprahov@yahoo.com, Kalin Dimitrov, Todor Marvakov) The dredging works in southern harbor, carried out by a floating crane Giant, were observed. The dredging area was c. 400 m long and up to 100 m wide. A layer was documented, containing Late Classical, Hellenistic, Late Antique and Mediaeval sherds. The Hellenistic sherds prevailed, including from amphorae of Rhodes, Thasos, Knidos and the Solokha Type. The finds included a terracotta brazier, a quern and a handle of a Rhodian amphora with a producer stamp of Soteridas of 233 – 220 BC.

UNDERWATER ARCHAEOLOGICAL EXPLORATIONS IN THE AQUATORY OF MESAMBRIA (Nayden Prahov – naydenprahov@yahoo.com, Kalin Dimitrov) Fifteen underwater archaeological expeditions were carried out between 1960 and 1984. Fortification structures were discovered to the north and northeast of the peninsula. In 2017, explorations were carried out from the northeastern side of the peninsula. Structures that were known from the previous explorations were rediscovered: a section of Late Antique fortification wall built of stones bonded with mortar, over 2.20 m wide, c. 15 m long; a rectangular tower, 6 m by 8 m in size, built of ashlars, some of them over 1 m long; a section of fortification wall built of ashlars, c. 2 m wide, c. 50 m long, situated to the east of the tower; a fortification wall built of ashlars, situated at c. 20 m to the east of the previous one; a section of fortification wall built of stone slabs, c. 2.80 m wide, c. 40 m long, with a rectangular tower, 5.50 m by 6 m in size. Sections of two new fortification walls were documented, the first one built of stone slabs, c. 1.80 m wide, and the second one in ¬_opus mixtum_. Underwater archaeological surveys were carried out to the northwest of the peninsula in the area where structures of the Late Classical and Early Byzantine periods were known. Sections of a Late Antique fortification wall built in ¬_opus mixtum_, c. 3 m wide, were documented.

UNDERWATER ARCHAEOLOGICAL EXPLORATIONS IN THE AQUATORY OF MESAMBRIA (Nayden Prahov – naydenprahov@yahoo.com, Kalin Dimitrov) During underwater diving surveys in the southern gulf of the peninsula, sectors of the early Byzantine fortification wall were discovered, built of stones bonded with mortar. A stone cylindrical segment of a column was discovered close to the coast. The rectangular fortification tower in the eastern gulf was cleaned. It was built of ashlars and measured 8 m by 8 m. The fortification wall to the east of the tower was also cleaned. It was situated at 2 – 4.50 m in depth and its inner and outer faces were built of ashlars. The wall was clearly visible at 35 m in length. Two monumental structures of piled stones were documented. The first one had a L-like layout and was c. 19 m wide, c, 3.50 m high and c. 35 m long. The second structure was c. 75 m long, up to 7 m wide and c. 1 m high. Probably, the structures were ancient breakwaters. Underwater diving surveys and excavations were carried out to the west of the Argirova Breakwater. Sectors of the Early Byzantine fortification wall, built in _opus mixtum_ and c. 3 m wide, were discovered parallel to the west of the structure of piled stones that was c. 60 m long. The geophysical explorations in the water area to the south of the peninsula continued; multi-beam echo-sounder and lateral scanning sonar were applied.

UNDERWATER ARCHAEOLOGICAL EXPLORATIONS OF MESAMBRIA (Nayden Prahov – naydenprahov@yahoo.com, Kalin Dimitrov) In the bay to the west of the Southern Breakwater, a sondage was carried out at the foundation of the eastern sector of the Early Byzantine fortification wall, documented in 2017 and 2018. The wall was documented along almost the entire gulf. The eastern sector of the wall is the best preserved part c. 15 m long. It was c. 2 m wide, built of stones bonded with mortar. Twelve parallel wooden posts were documented, vertically stuck into the clay layer below the foundation of the fortification wall. A cylindrical segment of a column was discovered in the central area of the bay, at 1.50 m below the sea level and close to the shore. In 2018, another segment was found there. In addition, ashlars were documented in the same area. To the east of the Southern Breakwater, the explorations of structures examined in 2017 and 2018 continued. The exploration of the rectangular fortification tower, 8 m by 8 m in size and situated at c. 3 m below the sea level, continued. The ashlars of the first row of the wall varied in size and shape. The tower was divided in two premises, 6 m by 8 m and 2 m by 8 m in size, by a wall built of smaller stones. There were two fortification walls to the west and to the east of the tower and their foundations were built of large ashlars. The tower and the walls belonged to the fortification system of the Classical period, with preserved length of c. 65 m. The fortification wall situated at c. 130 m from the coast was c. 1.20 m wide, built of large ashlars, up to 1 m by 0.50 m in size. It was preserved at c. 20 m in length. Five horizontal wooden beams incorporated among the ashlars of the first row were documented. A number of fragments from tegulae of the Corinthian Type dated to the Hellenistic period were also discovered.

UNDERWATER EXPLORATIONS AT MESAMBRIA (Nayden Prahov – naydenprahov@yahoo.com, Kalin Dimitrov) The peninsula and its water area were photographed with a drone. A digital terrain model was produced from the aerial photographs by means of photogrammetric processing. The photogrammetric and echo sounder digital terrain models were combined, thus obtaining a unified digital terrain model of the peninsula and its water area up to -18 m in depth. Diving surveys were carried out to the south of the Marine Station. A structure of ashlars with a visible size of 2.50 m by 6 m was discovered at c. 5 m from the coast and at c. 50 cm in depth. It was probably the foundation of a fortification wall. During diving surveys in the bay to the west of the Southern Breakwater, sectors of the Byzantine fortification wall and a drum of a column were discovered; thus the drums of columns discovered so far became three. Two ancient breakwaters were explored to the east of the Southern Breakwater. The first one had an L-shaped layout and was built of piled stones, including spolia: ashlars, some of them with grooves for iron clamps, two fragmentary and one intact drum of columns. The breakwater was c. 45 m long, c. 25 m wide and c. 3 m high. The second breakwater was built of piled stones. It was c. 82 m long, 8 – 15 m wide and c. 1.50 m high. A Late Antique structure was noticed at its foundation, thus giving a _terminus ante quem_ for the construction of the breakwater. The two breakwaters were documented photogrammetrically, and detailed terrain models and an orthophotomosaic were produced. The structures were photographed with a multibeam echo sounder and a bathymetric terrain model was produced.