The White Tower
The oldest part of the fortress is the so-called White Tower, which was completed in 1097. This keep was long the tallest building in London at 27.4 meters (90ft). Its walls are 4.6 meter wide.
The tower was whitewashed during the reign of Henry III, which gave the tower's facade its white appearance. Ever since the tower has been known as White Tower. The building has four domed turrets at each corner. Three of them have a square shape, the other is round, due to its spiral staircase. The round turret was long used as an observatory.