The Circus of Maxentius is an ancient part of a complex erected by emperor Maxentius on the Via Appia between AD 306 and 312. It is situated between the second and third miles of the Via Appia between the basilica and catacombs of San Sebastiano and the imposing late republican tomb of Caecilia Metella, which dominates the hill that rises immediately to the east of the complex.
The Circus itself is the best preserved in the area of Rome, and is second only in size to the Circus Maximus in Rome. The only games recorded at the circus were its inaugural ones and these are generally thought to have been funerary in character. They would have been held in honour of Maxentius' son Valerius Romulus, who died in AD 309 at a very young age and who was probably interred in the adjacent cylindrical tomb (tomb of Romulus). The imperial box of the circus is connected, via a covered portico, to the villa of Maxentius, whose scant remains are today obscured by dense foliage, except for the apse of the basilical audience hall, which pokes out from the tree tops. The complex was probably never used after the death of Maxentius in AD 312.
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.