Roman London was built on the north bank of the Thames, the site
of the modern City. The river, roughly in its present position
by the time of the Roman conquest, was probably tidal at London,
although tides may not have reached as far as Westminster (Milne
1985, 79-86). At high tide the river may have been as much as 1
km across and most of the south bank would have been submerged,
although there were important islands of dry land at Westminster
and Southwark. At low tide the channel would have shrunk to
about 275 m, still considerably wider than the river of today
which is about 200 m across. On its north side the Thames had
cut against a pair of low hills, and it was here that the town
was built. The western hill, Ludgate Hill, is now occupied by St
Paul’s Cathedral whilst that to the east (hereinafter referred
to as Cornhill) is presently surmounted by Leadenhall market.
These hills were separated by the valley of the Walbrook, the
upper parts of which remained marshland until reclaimed in the
Roman perio