Close to the Catacombs of San Callisto are the large and impressive Catacombs of Domitilla (named after Saint Domitilla), spread over 15 kilometres of underground caves.
The Domitilla Catacombs are unique in that they are the oldest of Rome's underground burial networks, and the only ones to still contain bones. They are also the best preserved and one of the most extensive of all the catacombs. Included in their passages are a 2nd-century fresco of the Last Supper and other valuable artifacts. There are almost 150,000 bodies buried in the Catacombs of St. Domitilla.
They are the only catacombs that have a subterranean basilica; entrance to the catacombs is achieved through this sunken 4th-century church, at via delle Sette Chiese 282. In the past, the basilica had become unsafe, and was abandoned in the 9th century. It was rediscovered in 1593, and much of it was reconstructed in 1872.
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.