Londinium was established as a civilian town by the Romans about four years after the invasion of AD 43. London, like Rome, was founded on the point of the river where it was narrow enough to bridge and the strategic location of the city provided easy access to much of Europe. Early Roman London occupied a relatively small area, roughly equivalent to the size of Hyde Park. In around AD 60, it was destroyed by the Iceni led by their queen Boudica. The city was quickly rebuilt as a planned Roman town and recovered after perhaps 10 years; the city grew rapidly over the following decades.
During the 2nd century, Londinium was at its height and replaced Colchester as the capital of Roman Britain (Britannia). Its population was around 60,000 inhabitants. It boasted major public buildings, including the largest basilica north of the Alps, temples, bathhouses, an amphitheater, and a large fort for the city garrison. Political instability and recession from the 3rd century onwards led to a slow decline.
At some time between AD 180 and AD 225, the Romans built the defensive London Wall around the landward side of the city. The wall was about 3 kilometers (1.9 mi) long, 6 meters (20 ft) high, and 2.5 meters (8.2 ft) thick. The wall would survive for another 1,600 years and define the City of London's perimeters for centuries to come. The perimeters of the present City are roughly defined by the line of the ancient wall.
Londinium was an ethnically diverse city with inhabitants from across the Roman Empire, including natives of Britannia, continental Europe, the Middle East, and North Africa.
In the late 3rd century, Londinium was raided on several occasions by Saxon pirates. This led, from around 255 onwards to the construction of an additional riverside wall. Six of the traditional seven city gates of London are of Roman origin, namely: Ludgate, Newgate, Aldersgate, Cripplegate, Bishopsgate, and Aldgate (Moorgate is the exception, being of medieval origin).
By the 5th century, the Roman Empire was in rapid decline, and in AD 410, the Roman occupation of Britannia came to an end. Following this, the Roman city also went into rapid decline and by the end of the 5th century was practically abandoned.