The Tower of London, on the hill on the north bank of the Thames, was built in 1078 under the official name "Her Majesty's Palace and Castle" and was originally a military castle built by William the Conqueror. From the 12th century, successive British kings built palaces, churches and state prisons here. The most important and oldest building of the Tower of London is the Normandy tower in the center of the fortress, making the main body of the entire complex known as the White Tower because of the milky stone. Four towers towering in four corners, three rounds, with spiral staircases at the corners that lead to the top floor. St John's Church in the White Tower is the oldest existing church in London and is a Normandy-style building. The center of Baitavi is surrounded by 13 towers, and the most famous is the Wakefield Tower, the Blood Tower, and the Bechham Tower. The Blood Tower was built in 1225 and was originally called the Garden Tower. It was renamed the Blood Tower at the end of the 16th century because of tragic events. It was used by the king to imprison political prisoners and the king's sworn enemies, and was a death row, and most of the people who were put to death in the tower were executed. As a heavily defended fortress and palace, the kings of England lived here for generations, and the crowning of the king to the Tower of London became a custom, with dungeons and swords showing ancient criminal law, and the oldest church in the 11th century. Its dome basement, the collection of kings of the crown crane stones, jewelry. Among them, the "Empire Crown" has 3,000 gemstones on it, the "African Star" gemstone in the center of the "Sceptre" weighs 530 carats, and the rubies known as the "Black Prince" are world-famous rare treasures.