During centuries, fortification walls and towers were built to protect ancient Nessebar. The first inhabitants on the peninsula were the Thracians who started to build these walls in the 8th century BC. From this period, a fortified wall and gate were found and can be seen today. After the decay of the Roman Empire, Byzantine rulers started an active construction work in the middle of the 5th century AD. The built walls were in style opus mixtum- an alternation of bricks and stone. Best preserved walls can be seen today near the city gate. The early Byzantine construction system was used in the middle ages as well.
Due to enemy war attacks, part of the walls were destroyed, but then quickly rebuilt. After the Ottoman rule in 1453, the fortification walls lost their significance and strategic importance and were left in ruins.
References:The ancient Argos Theater was built in 320 BC. and is located in Argos, Greece against Larissa Hill. Nearby from this site is Agora, Roman Odeon, and the Baths of Argos. The theater is one of the largest architectural developments in Greece and was renovated in ca 120 AD.
The Hellenistic theater at Argos is cut into the hillside of the Larisa, with 90 steps up a steep incline, forming a narrow rectilinear cavea. Among the largest theaters in Greece, it held about 20,000 spectators and is divided by two landings into three horizontal sections. Staircases further divide the cavea into four cunei, corresponding to the tribes of Argos A high wall was erected to prevent unauthorized access into the theatron and may have helped the acoustics, but it is said the sound quality is still very good today.
Around 120 CE, both theaters were renovated in the Roman style.