Agricola looked across the North Channel to Ireland, which could be conquered and held, he thought, by a single legion of his regular troops supported by auxiliaries. The Roman hold on Britain would then be much stronger.

Between 400 and 450 Christianity was established in the area by St Ninian, a bishop and a Briton, whose main church was at Whithorn in the Machars.
An almost equally early site is at Kirkmadrine in the Rhins where three early monumental stones commemorate three priests or bishops.

Meanwhile the Angles of Northumbria had extended their political power to Galloway. About 739 Pecthelm, who came from the south of England, became the first in a series of Anglian bishops to be elected to Whithorn. The name Whithorn is itself Anglian, meaning 'the white house.' The influence of the Irish church declined, but did not disappear. Little trace of the Angles is to be found in the Southern Rhins.

From about 800 Vikings from Scandinavia became active in the British Isles and Ireland. Some settled in the Rhins and became farmers or land owners. Place-names bear witness to their presence. The old form of the name Stoneykirk, for instance, is Stennaker, Norse for 'field of stones, stony field.'