Why the Tower of London Was Built on the Thames: Trade Control & Defense

William the Conqueror sited the Tower of London (begun 1078) on the north bank of the River Thames for two strategic reasons:

1. Trade control: The Thames was England's premier commercial artery; the Tower could tax, inspect, and regulate river traffic entering London.
2. Defense: Water on three sides (river + moat) made it a formidable stronghold against land and riverborne attack.

Over centuries it became a royal palace, prison, armory, mint, and treasury—but its original logic was hydraulic and military.