History: London, England, United Kingdom

It is likely that there was a harbour at the mouth of the River Fleet for fishing and trading, and this trading grew, until the city was overcome by the Vikings and forced to move east, back to the location of the Roman Londinium, in order to use its walls for protection. Viking attacks continued to increase, until 886 when Alfred the Great recaptured London and made peace with the Danish leader, Guthrum. The original Saxon city of Lundenwic became Ealdwic ("old city"), a name surviving to the present day as Aldwych, which is in the modern City of Westminster.
Middle Ages
With the collapse of Roman rule in the early 5th century, London was effectively abandoned. However, from the 6th century an Anglo-Saxon settlement known as Lundenwic developed slightly to the west of the old Roman city, around what is now Covent Garden and the Strand, rising to a likely population of 10–12,000. In the 9th century London was repeatedly attacked by Vikings, leading to a relocation of the city back to the location of Roman Londinium, in order to use its walls for protection. Following the unification of England in the 10th century London, already the country's largest city and most important trading centre, became increasingly important as a political centre, although it still faced competition from Winchester, the traditional centre of the kingdom of Wessex.