Satellite image of Scotland and Northern Ireland showing the approximate greatest extent of Dál Riata (shaded). The mountainous spine which separates the east and west coasts of Scotland can be seen.
Dál Riata or Dál Riada (also Dalriada) (/) was a Gaelic overkingdom that included parts of western Scotland and northeastern Ireland, on each side of the North Channel. At its height in the late 6th and early 7th centuries, it encompassed roughly what is now Argyll in Scotland and part of County Antrim in Northern Ireland. Both are now part of the United Kingdom.
In Argyll, it consisted of four main kindreds each with their own chief:
Latin sources often referred to the inhabitants of Dál Riata as Scots (Scoti), a name originally used by Roman and Greek writers for the Irish who raided Roman Britain. Later, it came to refer to Gaelic-speakers, whether from Ireland or elsewhere. They are referred to herein as Gaels, an unambiguous term, or as Dál Riatans.
The hillfort of Dunadd is believed to have been its capital. Other royal forts included Dunollie, Dunaverty and Dunseverick. Within Dál Riata was the important monastery of Iona, which played a key role in the spread of Celtic Christianity throughout northern Britain, and in the development of insular art. Iona was a centre of learning and produced many important manuscripts. Dál Riata had a strong seafaring culture and a large fleet.
Dál Riata is said to have been founded by the legendary king Fergus Mór (Fergus the Great) in the 5th century. The kingdom reached its height under Áedán mac Gabráin (r. 574–608). During his reign Dál Riata's power and influence grew; it carried out naval expeditions to Orkney and the Isle of Man, and assaults on the Brittonic kingdom of Strathclyde and Anglian kingdom of Bernicia. However, King Æthelfrith of Bernicia checked its growth at the Battle of Degsastan in 603. Serious defeats in Ireland and Scotland during the reign of Domnall Brecc (died 642) ended Dál Riata's "golden age", and the kingdom became a client of Northumbria for a time. In the 730s the Pictish king Óengus I led campaigns against Dál Riata and brought it under Pictish overlordship by 741. There is disagreement over the fate of the kingdom from the late 8th century onwards. Some scholars have seen no revival of Dál Riatan power after the long period of foreign domination (c. 637 to c. 750–760), while others have seen a revival under Áed Find (736–778). Some even claim that the Dál Riata usurped the kingship of Fortriu. From 795 onward there were sporadic Viking raids in Dál Riata. In the following century, there may have been a merger of the Dál Riatan and Pictish crowns. Some sources say Cináed mac Ailpín (Kenneth MacAlpin) was king of Dál Riata before becoming king of the Picts in 843, following a disastrous defeat of the Picts by Vikings. The kingdom's independence ended sometime after, as it merged with Pictland to form the Kingdom of Alba.
The name Dál Riata is derived from Old Irish. Dál, cognate to English dole and deal, German Teil, and Latin tāliō and descendants including French taille and Italian taglia, means "portion" or "share" (as in "a portion of land"); Riata or Riada is believed to be a personal name. Thus, the name refers to "Riada's portion" of territory in the area.
The Dalradian geological series, a term coined by Archibald Geikie in 1891, was named after Dál Riata because its outcrop has a similar geographical reach to that of the former kingdom.