So, the young farmer’s sons growing up in Rathdown between 300 AD and 700 AD, had a number of clearly-established career choices, if they chose to forsake the land. Some of their compatriots would have been in the Roman army, with exciting tales of adventure and new vistas. Others might have become involved in well-established trading routes. Still others may have been responsible for raids on Roman Britain.
There was even one other option. Increasingly, settlers from eastern and southern Ireland were setting up home in large numbers in the west of Britain, especially Wales, Cornwall and parts of Scotland. In addition to this random settlement pattern, an organised group migration took place in the fourth century. The Deisi people, centered in Munster and parts of Leinster, moved in large numbers to Dwyfed and Cardigan Bay in Wales. The Ogham script, characteristic of the Deisi, has now been found extensively on monuments in this area.
It would seem strange that the all-conquering Roman army would allow such settlement. However, troop numbers in the coastal region were extremely low, and it was also felt that the new settlers might act as a kind of buffer zone against further raids.
Cunliffe, Barry : Britain Begins, Oxford University Press.
de Paor, Maire & Liam (1958) Early Christian Ireland, Thames and Hudson, London.