United Kingdom of Great Britain and Northern Ireland

55（1 Jan.）　Roman General Julius Caesar invades Great Britain for the first time, gaining a beachhead on the coast of Kent. 

54　Caesar invades for the secnd time, gaining a third of the country. The two invasions are known as Caesar's invasions of Britain.

43　Aulus Plautius leads an army of forty thousand to invade Great Britain. Emperor Claudius makes Britain a part of the Roman Empire. This is known as the Roman conquest of Britain.

50   London is founded.

61   The wife of Celtic Briton king of the Icenitribe, Boudica's organized rebellion against the Romans is defeated.

122   Emperor Hadrian orders a wall to built to make Roman territory of Britain in the north.

197   Britain is divided into two parts - Britannia Superior, the southern part, and Britannia Inferior, the northern part.

206   Governor Lucius Alfenus Senecio repairs Hadrian's Wall and appeals for help from the Emperor against the northern tribes.

208   Emperor Septimius Severus and his son Caracalla take persnal command of the army in Britain.

209   Severus and Caracalla lead an expedition against the Caledonii, and build forts at Cramond and the Tay estuary.

210   Caracalla leads an expedition against the rebellious Maeatae tribe.

211   4 February, Severus dies at York, while preparing another expedition against the northern rebels. Caracalla, now Emperor, abandons territory north of Hadrian's Wall, and returns to Rome.

214   Britain divided into two provinces, Britannia Superior and Britannia Inferior, with administrative centres at London and York respectively.

参考：Wikipedia