For over 900 years the Tower of London has been standing guard over the capital . As a Royal Palace Fortress prison , place of execution arsena Royal Mint Royal Zoo and Jewel House . Construction of the Tower of London was initiated in 1070 by William the Conqueror, shortly after his victory at Hastings in 1066. The Tower was built to enforce the power of the king over the newly conquered region. The oldest part of the fortress is the so-called White Tower, which was completed in 1097.