<human>:  When was the Tower of London built?
<bot>: The Tower of London was built in the 11th century. It was a fortress that protected the City of London from invaders. The tower was built by William the Conqueror in 1078. It was originally called the White Tower. In the 15th century, the tower was renovated and renamed the "Tower of London" by King Henry VIII. The Tower of London is one of the most well-preserved medieval fortresses in the world.