Dál Riata

State · 540–899 CE · at its largest around 750 CE

A Gaelic kingdom spanning Argyll in western Scotland and the north of County Antrim in Ireland. Its monastery of Iona was a major centre of Christianity.

On its lands while it lasted

• Founding of Iona Abbey (563 CE): Monastery founded by the Irish monk Columba on Iona, which became a centre of Celtic Christianity and missionary work in Scotland.
• Edinburgh (601 CE): Capital of Kingdom of Scotland (1452–1608).

More on Wikipedia.