Because at the time that it was built, it was considered that any threat would either come from invaders ships sailing up the river or an army coming from the south which would have to cross the river to get to London. The original London Wall, which surrounded the city to protect it, started and finished at the Tower.
It was there already. London was built around the river.
The river Thames is England, and is the river that London is built on.
it was built in London, England over the Thames river
London
The Thames is a river flowing across London, Great Britain.
They were built at the south of the River Thames.
Because London is built on the ancient flood plane of the river Thames.
The Thames Barrier.
The globe thetaer was built on the south banks of river Thames in London,England.
It was the first bridge across the River Thames in London (built by the Romans nearly 2000 years ago) and was the only bridge across the Thames in London until 1729.
The only railway under the river Thames is parts of the London Underground (tube).
London, on the south bank of the Thames in Southark. [say 'suthock]