The invasions of Britain by Julius Caesar
The first Roman invasions of Britain were by Julius Caesar in 55 BC and 54 BC, with Caesar using the Britons support for the Celts in Gaul as an excuse to attack. The first in 55 BC was little more than a raid in force by two legions. The second was in greater strength, but again Julius Caesar did not leave a permanent presence and left in the autumn.
Both narrowly avoided disaster, and it's unlikely that the promised tributes were ever paid. But the expeditions gave Julius Caesar massive prestige for extending Roman influence to the edge of the known world. The tales of Britons fighting from chariots would have reminded the citizens in Rome of the tales of Homer and added to the mystique of the Isles. Julius Caesar was therefore awarded a great triumph on his return to Rome, out of proportion to the material success of the invasions.
It would be nearly a century before the Roman legions returned, but over the coming years there was a big increase in Roman influence in Britain. Especially in the South East where trading with Roman merchants greatly epanded.
The invasion of Britain by Emperor Claudius.
The next invasion of Britain was under the emperor Claudius. Claudius needed to win personal credibility with the army, the prestige of campaigning in Britain would give him this. The backbone of the force was four legions: the II Augusta and the XIV Gemina and probably the IX Hispana and XX legion. In addition there would have been approximately the same number of auxiliaries making a total force of about 40,000 troops. This force was under the command of Aulus Plautius, who would become the first Roman governor of Britain
The invasion nearly came to grief before it started when the troops feeling they were being sent beyond the edge of the known world refused to board the ships. Claudius sent his freedman Narcissus to investigate. At first the troops were outraged by being addressed by an ex slave, but eventually he got them to obey their orders. The delay did have one advantage as the Britons sensing that the invasion was off had dispersed their forces
The crossing was made in three divisions, one landing at Richborough, and one probably at Chichester. The position of the third landing is unknown. Plautius initially had problems bringing the Britons to battle, as the Britons withdrew into the swamps and woods, but was eventually able to win a number of victories over them. Late in the campaigning season the Emperor Claudius himself came over to Britain along with reinforcements (which even included some elephants).
Defeat of the Britons
The Britons were not a unified force, but a collection of often warring tribes. Although many of these tribes were hostile to the Romans, others were friendly or even allied to the Romans. These included King Cogidubnus, who controlled the area around Chichester (which gave the Romans a secure base on the British side of the Channel), and initially the Icenii in Norfolk. The Brigantes who controlled the a huge part of the North of England (including the area on which Hadrian wall was to be built) were also initially allied to the Romans. Paradoxically both the Icenii and the Brigantes were to cause a great deal of problems for the Romans in the future.
By the time Plautius returned to Rome in 47 AD the conquest of the South and East of Britain was complete. The new governor Publius Ostorius Scapula at first tried to consolidate these gains. But his plans were disturbed by the first Icenii revolt. Having crushed this, Ostorius advanced into North East Wales. Once again he was forced to change his plans, this time to deal with disturbances among the Brigantes.