When the Romans invaded Britain in 43 AD, they crossed in three divisions, under the command of Aulus Plautius. The ships are thought to have traveled from Boulogne to what is now Richborough, on the east coast of Kent.
The Romans operated on a shock and awe type of warfare and eleven tribes of southeast Britain surrendered to Claudius. The Romans moved west and north from there, establishing their new capital at Camulodunum.
It wasn’t until late in 47 AD that the new governor of Britain, Ostorius Scapula, began a campaign against the tribes of modern day Wales. http://en.wikipedia.org/wiki/Roman_conquest_of_Britain
“The ever-pugnacious Caratacus – the Caradog of Welsh legend – moved north to carry on the fight in the territory of the Ordovices in Anglesey and Caernarfon. There, in 51AD, he was defeated and his family captured.”
Later, the Silures defeated the forces sent against them in 52AD, and the grip of the Romans on their new British territory remained a troubled one. Fresh campaigns in 57 and 60AD struck deep into Welsh territory.
The latter campaign was directed at the seat of druidical power in Wales, the Isle of Anglesey. According to the Roman historian Tacitus, the legionnaries doffed their clothes and swam naked across the Menai Straights to do battle with the druid-led Celts.” .” http://www.britainexpress.com/wales/history/roman-invasion.htm
“The novelty of the fight struck the Romans with awe and terror. They stood in stupid amazement, as if their limbs were benumbed, riveted to one spot, a mark for the enemy. The exhortations of the general diffused new vigor through the ranks, and the men, by mutual reproaches, inflamed each other to deeds of valor. They felt the disgrace of yielding to a troop of women, and a band of fanatic priests; they advanced their standards, and rushed on to the attack with impetuous fury. The Britons perished in the flames, which they themselves had kindled. The island fell, and a garrison was established to retain it in subjection. The religious groves, dedicated to superstition and barbarous rites, were leveled to the ground. In those recesses, the natives [stained] their altars with the blood of their prisoners, and in the entrails of men explored the will of the gods.” http://www.bukisa.com/articles/37180_the-roman-invasion-of-wales#ixzz1GzLHSv8g
Just when it looked as if the Romans would be able to subdue the Welsh tribes, a revolt by the Iceni in Norfolk broke out, led by their queen, Boudicca (Boadicea). The Roman forces were diverted, and the Welsh territory remained under very tenuous Roman control for several years.” http://www.britainexpress.com/wales/history/roman-invasion.htm
Despite this great victory on Anglesey, the Romans continued to have difficulties with the people of northwest Wales. This is evidenced by the number of military installations in the area and the lack of villas.
“Throughout the second half of the 4th century the Empire became increasingly unstable; barbarian attacks on the borders increased, and it seems that the legions were gradually withdrawn from Wales to counter threats on the continent.
By 390AD there were probably no Roman troops remaining within the borders of Wales. In the next few decades most of the legionnaries in England followed and Brittania was esentially undefended.
The Irish saw their chance; in 405 pirates under Nial ravaged the western coast, and may have precipitated a fresh influx of Irish settlers.” http://www.britainexpress.com/wales/history/roman-invasion.htm