It was the Romans who first built a city where London stands today, by bridging the river Thames and constructing a road network to connect Londinium with the rest of the country. From around AD50 to AD410 – a period as long as that which separates Queen Elizabeth I from our present Queen – Londinium was the largest city in Britannia. It was pre-eminent as a port, and goods were imported from the far reaches of the Roman Empire.
The commander of the Roman troops was Aulus Plautius. He pushed his men up from their landing place in Kent towards Colchester, then the most important town in Britain. The Roman advance was halted by the Thames, and Plautius was forced to build a bridge in order to reach his destination. This first "London Bridge" was recently excavated, and found to be only yards from the modern London Bridge. The Roman bridge proved a convenient central point for the new network of roads which soon spread out like a fan from the crossing place and allowed the speedy movement of troops. The Roman settlement on the north side of the bridge, called Londinium, quickly became important as a trading centre for goods brought up the Thames River by boat and unloaded at the wooden docks by the bridge.
Just 18 years after the arrival of the Romans, Boudicca, queen of the Iceni tribe of present-day East Anglia, launched her rebellion against the new rulers of Britain. The new trading centre of Londinium was one of her primary targets, and her warriors levelled the burgeoning city and killed thousands of the traders who had begun to settle there. Tacitus wrote that "Londinium ... though undistinguished by the name of a colonia, was much frequented by a number of merchants and trading vessels." In the years after the uprising, the provincial administration of Britain moved from Camulodunum (modern Colchester in Essex) to Londinium. The city was then quickly rebuilt, with a cluster of timber-framed wooden buildings surrounding the imposing Roman civic buildings. The city continued to grow in size over the next century, reflecting the increasing importance of trade within and to Britain.
By the middle of the second century AD, Londinium possessed the largest basilica (town hall) west of the Alps, a governor's palace, a temple, bathhouses, and a large fort for the city garrison. Gracechurch Street, in the City, runs through the middle of the old Roman basilica and forum (market place). One of the finest Roman remains in London is the 2nd century Temple of Mithras (mithraism was a form of religion, popular amongst Roman soldiers). It was found near Walbrook, during construction work in the 20th century, and moved to Temple Court, Queen Victoria Street. Artifacts recovered from the excavation of the temple are now in the Museum of London. Currently plans are underway to move the temple back to its original location. London's Roman amphitheatre was recently discovered and the remains can be seen in the basement exhibition space of the Guildhall Gallery.
In approximately 200 AD, a defensive wall was built around the city (the 'London Wall') - 3 miles long, 20 feet high and 8 feet thick. For well over a millennium the shape and size of London was defined by this Roman wall. The area within the wall is still known as "the City", London's financial district. Traces of the wall can be seen in several sections of its perimeter.
London continued its growth during the late Roman Empire, and at its peak the population probably numbered 45,000. In the fourth century AD Londinium changed its name to Augusta. As the Roman Empire began to dissolve in the early 5th century, large numbers of barbarians penetrated Gaul and Spain and seriously weakened communication between Rome and Britain, on the western edge of the Empire. British troops elected their own leaders - the last of these, Constantine III, declared himself to be emperor of the Western Roman Empire - and took an expeditionary force across the Channel, leaving Britain short of troops. In 410, the Romano-British authorities dropped their allegiance to Constantine and appealed to Emperor Honorius for help. He told them that the Britons would have to look after their own defences, meaning effectively that the Roman occupation of Britain officially came to an end.
After the fall of the Roman Empire, Britain became increasingly vulnerable to attack by Germanic invaders, namely Angles, Saxons, Jutes and Frisians. There is very little evidence - either historical or archaeological - of what happened to London in this sub-Roman period. However, chaos in the collapsing Roman Empire and Roman Britain meant that long distance trade broke down, wages of Imperial officials were not paid, and London declined drastically.