Londinium

Roman London (Londinium) was established around 43 CE. It served as a major commercial centre for the Roman Empire until its abandonment during the 5th century. The name "Londinium" is thought to be pre-Roman (and possibly pre-Celtic) in origin. Following its foundation in the mid-1st century, early Roman London occupied a relatively small area, roughly equivalent in size to Hyde Park at 350 acres (1.4 km2). The 19th-century antiquarian Roach Smith estimated its length from the Tower of London west to Ludgate at about one mile; and from London Wall in the north to the Thames bank around half a mile.

In around 60, little more than ten years after Londinium was founded, it was sacked by the Iceni led by their queen Boudica. Excavation has revealed extensive evidence of destruction by fire in the form of a layer of red ash beneath the city at this date. The city was rebuilt as a planned Roman town and recovered after perhaps ten years. During the later decades of the 1st century, Londinium expanded rapidly and quickly became Roman Britain's largest city. By the end of the 1st century, Londinium had replaced Camulodunum (modern Colchester) as the capital of Roman Britain. During the 2nd century, Londinium was at its height. Emperor Hadrian visited in 122, and probably as a result a number of impressive public buildings were constructed. At some point soon afterwards, a major fire destroyed much of the city. In the second half of the 2nd century, Londinium appears to have shrunk in both size and population. Although Londinium remained important for the rest of the Roman period, it appears never to have recovered fully from this slump, as archaeologists have found that much of the city after this date was covered in dark earth, which remained undisturbed for centuries.

Some time between 190 and 225, the Romans built the London Wall, a defensive wall around the landward side of the city. Along with Hadrian's Wall and the road network, the London Wall was one of the largest construction projects carried out in Roman Britain. The wall was about 5 kilometres (nearly 3 miles) long, 6 metres (20 ft) high, and 2.5 metres (8 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.