The Romans brought the art of making domestic gardens to the British Isles. No definite archaeological evidence of the layout of Roman gardens has been found in London but there are several exhibits in the Museum of London of interest to gardeners (1) models of Roman houses with courtyard houses (2) Roman gardening tools used in Britain (3) a drawing of the Roman Provincial Governor's headquarters. This building was located on the site of Canon Street Station, directly below what is now the forecourt of the station. It is sometimes described as the Governor's Palace but is now thought to have been a Praetorium - an army HQ. Evidence of a pool has been found and, though this implies the existence of a garden, no direct evidence or Roman horticulture in London was uncovered when Canon Street Station was being rebuilt.
Museum of London, 150 London Wall, London, Greater London, England