Alūksne Castle was built in 1342 by Teutonic Knights on the largest of the islands in the Lake Alūksne and called Marienburg (after Mary, the mother of Jesus). The first castle was constructed by the Landmeister Burkhard von Dreileben. It was part of a major reinforcement of the Eastern border of Livonia, the same year another major castle nearby (in Vastseliina) was founded as well.
The initial castle was built of wood. Later, the outer walls were constructed of fieldstone and the convent house of bricks. The plan is in many ways similar to that of Viljandi Castle, including the convent building with a flanking tower. The outer wall originates partly from the same time as the convent house, partly from later periods, notably from the time of the political tensions in early 16th century. The main gate, protected by two round towers, is also of late medieval origin. Later, at the end of 17th century, the castle was supplied with ravelines and ramparts.
The strength of the castle was repeatedly proven by repelling a number of attacks in 16th century. Alūksne was captured by the troops of Ivan IV of Russia in 1560 during the Livonian War. It was incorporated into the Polish-Lithuanian Commonwealth in 1582. The town became part of the Swedish Empire in 1629.
After the fall of the Old Livonia, the castle remained habitable. It was finally destroyed 1702 in the Great Northern War by its Swedish garrison to avoid falling in the hands of Russians. The ruins remained largely untouched. Today, it houses an open-air scene and forms a part of a recreational area of the Pils (Castle) Island.
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.