The amphitheatre of Catania is the most complicated and largest of all the amphitheatres in Sicily. It was built in the Roman Imperial period, probably in the 2nd century AD, on the northern edge of the ancient city at the base of the Montevergine hill. Only a small section of the structure is now visible, below ground level, to the north of Piazza Stesicoro.
The external diameter was 125 x 105 metres, while the external circumference was 309 metres. From the theatre's dimensions it can be calculated to have held 15,000 spectators and almost double that number with the addition of wooden bleachers for standing spectators. According to an uncertain and unconfirmed tradition, it was intended that naumachiae (staged sea battles) take place in the amphitheatre, using the ancient aqueduct to fill the arena with water.
According to Cassiodorus, in the 5th century, Theodoric, King of the Ostrogoths, allowed the inhabitants of the city to spoliate the theatre for building material for the construction of stone buildings.
In the 13th century, according to tradition, the amphitheatre's vomitoria (entranceways) were used by the Angevins to enter the city during the Sicilian Vespers. In the following century, the entrances were walled up and the ruins were incorporated into the Aragonese fortifications (1302).
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.