The river thames is the main approach to london from the east.1000 years ago William the Conqueror decided to build a strong fortress to protect the City of london,which he had just conquered.the towerof london was one of the first and most impressive castles built after the Norman invasion of England in 1066. since the times of Wiliam the first kings have built and extended the tower of london and used it for many purposes.the tower has been used as a royal palace,an observatory,an arsenal,a state prison,and many famous and infamous people have been executed within its walls.it is now a museum.for many visitors the principal attractionis the Crown Jewels,the finest. precious stones of the nation.a fine collection of armour is exhibited in the Keep.the security ot the Tower is ensured by a military garrison and by the Yeoman Warders or "Beefeaters" who still wear their picturesque Tudor uniform.