Londinium is the name the Romans gave to London around 43 AD, when they finally made a settlement of significance around the Thames River.

By the middle of the second century AD, Londinium possessed the largest basilica west of the Alps, a governor's palace, a temple, bathhouses, and a large fort for the city's garrison.

One of the best Roman remains in London is the 2nd century Temple of Mithras. About the year 200 AD a defensive wall was built around the city. For well over a millennium the shape and size of London was defined by this Roman wall. The area within the wall is now "the City", London's famous financial district. Traces of the wall can still be seen in a few places in London.