The Romans built a fortress in AD 106 on the site of an earlier Thracian settlement and kept its name, Durostorum. The earliest saints of Bulgaria are Roman soldiers executed at Durostorum during the Diocletian Persecution (303–313), including St. Dasius and St. Julius the Veteran. Durostorum became an important military center of the Roman province of Moesia, and grew into a city at the time of Marcus Aurelius. It became the seat of a Christian bishopric and a center of Christianity in the region. Auxentius was expelled from Durostorum by an edict of Theodosius depriving Arian bishops in 383, and took refuge at Milan where he became embroiled in controversy with St Ambrose.
The Roman general Flavius Aëtius was born in the town in 396. When the Roman Empire split into the Eastern and Western empires, the town became part of the Eastern Roman Empire. As part of the Bulgarian Empire Durostolon was known as Drastar in Medieval times.
Today the massive fortifications of the ancient town are partially exhibited in the city park.
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.