Steinerne Brücke in Regensburg is a 12th-century bridge across the Danube linking the Old Town with Stadtamhof. For more than 800 years, until the 1930s, it was the city's only bridge across the river. It is a masterwork of medieval construction and an emblem of the city.
Charlemagne had a wooden bridge built at Regensburg, approximately 100 metres east of the present bridge, but it was inadequate for the traffic and vulnerable to floods, so it was decided to replace it with a stone bridge. The Stone Bridge was built in only eleven years, probably in 1135–46. Louis VII of France and his army used it to cross the Danube on their way to the Second Crusade. It served as a model for other stone bridges built in Europe in the 12th and 13th centuries. For centuries it was the only bridge over the river between Ulm and Vienna, making Regensburg into a major centre of trade and government.
The Stone Bridge is an arch bridge with 16 arches. At the south end, the first arch and first pier were incorporated into the Regensburg Salt Store when it was built in 1616–20, but remain in place under the approach road to the bridge. An archaeological investigation was performed in 2009, and revealed fire damage during the Middle Ages.
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.