The bishop castle of Haapsalu was built in the 13th century. It was the main residence of the Bishop of Läänemaa. The Läänemaa bishopric was created as a state of the Holy Roman Empire on 1 October 1228.
Construction, widening and reconstruction of the stronghold went on throughout several centuries, with the architecture changing according to the development of weapons. The stronghold achieved its final dimensions under the reign of Bishop Johannes IV Kievel (1515–1527). The western side of the castle houses a 29-metre watchtower dating from the 13th century, later used as a bell tower. The walls were later raised to 15 metres. The inner trenches and blindages, which were built for cannons and as a shelter from bombing, date back to the Livonian War (1558–1582), but it was during this war that the stronghold was severely damaged. The walls of the small castle and the outer fortification were left partly destroyed.
In the 17th century, the castle was no longer used as a defensive building by the Swedes who now ruled the Swedish Estonian Province. In the course of the Great Northern War in 1710, Estonia fell under Russian rule and the walls were partially demolished at the command of the Peter I of Russia, turning the castle in effect into ruins.
The Cathedral of Haapsalu is attached to the castle. It was the official chair of the Bishop, was situated and where the Chapter of the Bishopric worked. It is the biggest single-naved church in the Baltic countries, with its 15.5-metre-high domical vaults and an area of 425 m2. The Dome church was probably built in the 1260s, following the style of the Cistercian Order. The round baptism chapel on the eastern side of the church was built in the 14th or 15th century and is the site of a famous legend. On moonlight August nights the shape of a Lady in White appears on the inside wall of the chapel as the moon shines through the chapel window. This Lady is said to have been a woman who was in love with the abbot and entered the castle against his orders, therefore having been walled in there alive as a punishment. The church has been restored and it is again in active use by the local congregation of the Estonian Lutheran Church since 1990.
References: Wikipedia, Castles.info
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.