Boppard’s most famous sight is a castrum, a Roman Fort. The military camp of Bodobrica was established here in 360 AD. It is thought to be the best preserved example north of the Alps today. It once had 28 towers, and was a commercial centre as well as a fort. It was 308 × 154 metres and formed a rectangle of 4,7 hectare. The walls were 3 metres thick to the land side and 2,5 metres thick to the Rhine side. With a height of 9 metres and 20 horse-shoe shaped towers to the land side, each 27 metres apart, the wall made a very powerful fortification.
The fort can be wandered around freely and it is in remarkably preserved condition. Many of the finds that have been recovered and excavated from the site can be found in the Boppard museum.
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.