Shortly after the second Roman invasion of Britain, Verulamium was established around the Iron Age settlement of Verlamion. The destruction of the settlement by Boudicca afforded the opportunity to apply Roman town planning principles to the city. Verulamium became one of the largest Roman cities in Britain (at least by area). Unlike many other Roman towns and cities, Verulamium's sub-surface remains were largely undisturbed until the 19th century, allowing modern archaeologists to map the layout with more easy and accuracy than elsewhere. But much remains to be done, and work continues.