The Teatro Romano in Trieste was built in the first century BC and expanded in the second century AD. It had seats for from 3,500 to 6,000 visitors. It was probably built by the Trieste Quinto Petronio Modesto , prosecutor Emperor Trajan.
Over the centuries, the theater was left under the houses that were built above. Considered lost, it was identified in 1814 and unearthed in 1938 during the demolition of this part of the old city. The statues and inscriptions found in the excavations are kept in the San Guisto Castle.
Nowadays Teatro Romano is still occasionally used for outdoor summer shows.
FYI this is not an amphitheater because it is not in the round. It is simply a theater.
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.