Where did the Romans build London?

Good morning, ladies and gentlemen, welcome to River Thames. The 352-kilometer-long Thames is the longest river in England. It is a little river compared with the Nile, Amazon, or Mississippi. Yet, the Thames is unique in shaping the history of England.
    When the Romans conquered England, there were only marshy banks along the Thames. Like the people who had been living along the river,(11)they used the Thames as a highway and built the city London on its north bank.
    Today, the Thames means different things to different people.(12)It is, for example, a "sporting river" to rowers, but a "working river" for men of commerce. And painters and writers regard the Thames as a source of inspiration.(13)While being a great benefit to London and Londoners, the Thames can be a dangerous enemy. Chief among its dangers is flooding. To prevent the river from flooding, the world’s largest movable flood barrier was built in March, 1972. The barrier’s gates can stand eighteen meters above the river’s surface when the flood strikes.