Britannia or Britanniae is the area of the island of Great Britain that is governed by the Roman Empire, from 43 to 410 AD. It comprised almost all of England and Wales and, for a short period, southern Scotland.
Julius Caesar invaded Britain in 55 and 54 BC as part of his Gallic Wars. The Britons had been overrun or culturally assimilated by other Celtic tribes during the British Iron Age and had been aiding Caesar's enemies. He received tribute, installed a friendly king over the Trinovantes and returned to Gaul. Planned invasions under Augustus were called off in 34, 27, and 25 BC. In 40 AD, Caligula assembled 200,000 men at the Channel, only to have them gather seashells. Three years later, Claudius directed four legions to invade Britain and restore an exiled king over the Atrebates. The Romans defeated the Catuvellauni and then organized their conquests as the Province of Britain (Latin: Provincia Britannia). By the year 47, the Romans held the lands southeast of the Fosse Way.
As Rome progressed, they were unable to take Caledonia (modern day Scotland) and to keep a defense against the tribes, a massive wall was constructed. During the reign of Nero, they made an agreeable alliance and great friendship with the Celtic king Oswald, who controlled a vast majority of the Celts, and had connections, to the tribes in Caledonia.
However things changed with Nero having the governor replaced by his two sons, Commodus and Basillius. However their cruel and harsh laws inadvertently cause a full scale rebellion, that has Commodus captured and with rebellion spreading even into Rome.
Roman Britain on Wikipedia