The Abbey of St. Bertin was a Benedictine abbey, but today in ruins (the town's town-hall was built with stone from the abbey in 1834) and open to the public. It was dedicated to its second abbot, Saint Bertin.
The monastery was founded on the banks of the Aa in the 7th century by the bishop of Thérouanne, who sent the monks Bertin, Momelin and Ebertram from Omer to proselytize among the pagans in the region. The Abbey of St. Bertin soon became one of the most influential monasteries in northern Europe and ranked in importance with Elnon Abbey and the Abbey of St. Vaast. Its library included the codex of Aratea of Leyde, from which two copies were made. The Annals of St Bertin are an important source of the 9th-century history of Francia.
Already in the 9th century the abbey had a priory in Poperinge. A Romanesque church was constructed in the mid-11th century. It was 25m high, with a 48m high tower, and included a large 14th century semi-circular sanctuary with five side-chapels. It served as a model for the church, whose construction was not completed until the beginning of the 16th century.
From the 12th century the abbey had the right of appointing the priest at Lissewege and Ruiselede (1106). William Clito was buried here in 1128. The abbey had a 'refuge-house' in the now-demolished Sint-Lodewijkscollege in Bruges. The abbey had its greatest flourishing from its inception until the 13th century, though it survived until it was shut down at the French Revolution.
In 1830 the commune demanded the demolition of the church, though they spared the tower, which they strengthened with a buttress in the nave (still visible). However, the tower was weakened by bombardment of the town centre in World War II and collapsed in 1947, leading to the abandonment of the site.
The abbey is known for its Latin-written cartulary (Chartularium Sithiense) whose first part is attributed to Folquin (died in 855 in Esquelbeques).
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.