Rome under Claudius invaded Britain in 43AD, and Roman London, or Londinium, was founded in c. 47-8, as evidenced by dendrochronological or tree-ring dating of timbers from a Roman drain uncovered during archaeological excavations at No. 1 Poultry. The city was sited in a strategic position on high ground overlooking the Thames, at the lowest crossing-point on the river, and at a point at which it was also still tidal, enabling easy access to the open sea, and the empire beyond the sea (*). If Rome was built on seven hills, Roman London was built on two, Ludgate Hill to the west, and Cornhill to the east, with the valley of one of the Thames tributaries – the Walbrook – in between.
(*) There is some evidence that the tidal head moved downstream in the later Roman period, and that some port facilities followed it, from the City eastward toward Shadwell and Ratcliff.