London's situation on the Thames meant that it remained an significant trading centre even after it suffered after decline when the Romans left. From the early seventh century, London began to regain importance again. In this period the first St Paul's Cathedral was built, and traders were increasingly attracted to the river port. The Vikings were drawn by its wealth during their ninth-century raids, attacking it several times. In 851 AD they sailed up the Thames and burned the city to the ground.

Alfred gained control over London in 886 AD, but after his death, it fell for a time under Viking control again. Finally, London came under control of the King of England when Knut ascended the throne in 1017. Though Winchester was the capital of England, as the ancestral seat of the house of Wessex, royal control was increasingly centred on London. This was confirmed when Edward the Confessor moved his court there, and refounded the abbey at Westminster where his successors were thenceforth crowned.