The town-fortress called Nessebar /Mesembria/ is one of the most ancient cities in Europe. It was founded on a rocky peninsula 850m long and 300m wide. The area is around 25 ha and is connected with the main land through a narrow embankment, a road 400m long. During the existence of the city fortress walls and facilities were repeatedy built, which made the peninsula inaccessible.
The first inhabitants on the peninsula – the Thracians, started the fortification of the settlement in the 8th century BC. A gate found from this period was made of hewn stone joined by mud. As seen the remained wall today is 2 m high. During the time of Hellenistic colonization (as from 6th century BC) the colonists from Megara built a new wall in the end of the 5th C. and the beginning of the 4th C. BC till the 3rd C. BC. Big stone blocks were used, their face sides being specially polished, placed in line, without any solder. The inner part of the wall was felled with broken stones and soil. The Greek wall was well studied in the west part of the town. It can be seen that in some places it covers the Byzantine one.
Messambria being conquered by the Romans, the found defense system was preserved and used during the following centuries. After the decay of the Roman Empire the Byzantine rulers undertook an active constructional work and in the middle of the 5th century AD a new fortified wall has been built in “opus mixtum” – alternation of stones and bricks. The best-preserved part of it can be seen today near the city gate, opposite to the strip. Here the wall was faced with big orthogonal hewn stone blocks. The gate was flanked with two square towers on both sides of which round and semicircular towers were symmetrically placed. Two gates – a drawbridge like one and a twin leafed gate closed tightly the access to the town.
During the Early Byzantine period a fortified wall was built on the south – west coast, near the port. In the time of war attacks of enemies part of it was destroyed seriously but it was quickly rebuilt. The first reconstruction was dated to the end of 6th century and the beginning of the 7th century, after the attacks of the Avars. In the end of the 9th century during the reign of Khan Krum, the wall was rebuilt of bricks. In the end of the 11th century the defense system was repaired once again. During the reign of Tsar Ivan Alexander the walls were reconstructed. After the town fell under the Ottoman yoke in 1453, the defense system lost its strategic importance and, left without any special cares and gradually declined.