The Roman conquest of Britain in 55 BC and most of Britain's subsequent incorporation into the Roman Empire stimulated development and brought more active contacts with the rest of Europe. As Rome's strength declined, the country again was exposed to invasion--including the pivotal incursions of the Angles, Saxons, and Jutes in the fifth and sixth centuries AD.

The invasion of Britain that led to it becoming a province of the Roman Empire took place during the reign of Emperor Claudius, in 44 AD.

Earlier expeditions, notably by Julius Caesar, had not formally absorbed Britain into the empire and had been of variable success, though military remains from a pre-44 period suggest considerable Roman influence before the invasion took place.

For much of the history of Roman Britain, a large number of soldiers were garrisoned on the island, requiring that the emperor station a trusted senior man as governor of the province. Consequently, a number of future Roman emperors served as governors or legates in this province, including Vespasian, Pertinax, and Gordian I.

When emperor Hadrian reached Britain on his famous tour of the Roman provinces around 120 AD, he directed an extensive defensive wall, known to posterity as Hadrian's Wall, to be built close to the line of the Stanegate frontier.

During the following years the fronteer changed a number of times, occasionally moving further, to Northern Scotland, and at other times the Roman legions retreated to more defensible locations further South.

By the third century, Britain's economy was diverse and well-established, with commerce extending into the non-Romanised north. The design of Hadrian's Wall required the need for customs inspections of merchants' goods.

During Roman rule, an extensive network of roads, many of which are still in use today, as well as water and sewage systems were built.

Because of the prior rebelions of British governors, Emperor Septimius Severus tried to solve the problem of powerful and rebellious governors by dividing the existing province into Upper Britain and Lower Britain. This kept the potential for rebellion in check for almost a century, a period often called the Long Peace.

Following his conquest from a rebellious governor, emperor Constantius arrived in London in 293 AD, to receive the victory and chose to divide the island further, into four provinces: Maxima Caesariensis (based on London), Britannia Prima, Flavia Caesariensis and Britannia Secunda.

The earliest capital of Roman Britain was probably Colchestery, but it was soon eclipsed by London with its strong mercantile connections.

Constantius, part of the 3rd century Roman tetranchy, i.e., the rule of each of four Roman regions by one of four emperors, Constantius Chlorus rulled Britain. His son Constantine succeded him upon his death on 25 July 306, and used Britain as his base to subdue the other ceasars and become sole ruler of the empire. He then moved the capital to Byzantium, renaming it New Rome and Constantinople, where he died shortly after converting to Christianity.