The Abbey of St. Martin, established in 1124 in Laon in northern France, was one of the earliest foundations of the Premonstratensian Order. Along with Cuissy Abbey and Floreffe Abbey it counted as one of the primarii inter pares, or senior houses, of the order.
The Premonstratensian community was founded by Barthélemy of Jur, bishop of Laon, in co-operation with Saint Norbert of Xanten, who settled it with twelve canons from Prémontré Abbey. It took over the site of an earlier college of canons regular, established in the Carolingian period, which had fallen into decay.
It was dissolved in the French Revolution. The church of St. Martin in Laon, dating from mid to late 12th century, is still in use as a parish church. The former monastic buildings were converted into a hospital in 1810.
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.