score:24
The Roman conquest of Britain was undertaken in 43 CE by four legions:
These same legions still comprised the garrison a dozen years later during the uprising by Boudicea
Legio II Augusta remains in Britain until at least the 3rd century.
Legio IX Hispana is sent to Germania sometime between 108 and 130 AD.
Legio XIV Gemina is sent to the Balkans in AD 67.
Legio XX Valeria Victrix campaigned in Gaul briefly in AD 196 under Decimus Clodius Albinus before returning to Britain. It is believed to have then remained there until AD 407 until recalled by the usurper Constantine III.
Legio VI Victrix was assigned to northern Britain in AD 119 by Hadrian, and performed much of the construction of both Hadrian's Wall and the subsequent Antonine Wall.
This map of the Roman Empire in AD 125, with the location of all then extant legions, shows the Britain garrison at that time as comprising the legions:
Upvote:22
Actually, no Roman legions appear to have been based in London.
There was a fort in the north-west of the Roman city, built early in the second century, which could have held a garrison of about 1000 soldiers. However, this was the guard available to the governor of the province, rather than any particular legion.
In fact, five legions are known to have served in Britain:
Of the legions known to have served in Britain, Legio II Augusta, Legio IX Hispana, Legio XIV Gemina, and Legio XX Valeria Victrix were involved in the Claudian conquest of the province, while Legio VI Victrix was relocated to Britannia by the Emperor Hadrian in 119 AD.
None of these legions are known to have been based in Londinium at any time.
As a point of interest, the best-surviving part of Londinium's Roman Fort is its western gateway, which is preserved within a car-park under London Wall (the road):
Visit's are arranged by the Museum of London (usually with free entry on Open House London weekends).