Kingdom of Dublin

The Vikings invaded the territory around Dublin in the 9th century, establishing the Norse Kingdom of Dublin, the earliest and longest lasting Norse kingdom in all of Europe outside of Scandinavia, excepting the so-called Kingdom of Mann and the Isles. This corresponded to most of present-day County Dublin. The Norse referred to the kingdom as Dyflin, which is derived from Irish: Dubh Linn meaning "black pool". The first reference to the Vikings comes from the Annals of Ulster and the first entry for 841AD reads: "Pagans still on Lough Neagh". It is from this date onwards that we get references to ship fortresses or longphorts being established in Ireland. It may be safe to assume that the Vikings first over-wintered in 840–841AD. The actual location of the longphort of Dublin is still a hotly-debated issue. Norse rulers of Dublin were often co-kings, and occasionally also Kings of Jórvík in what is now Yorkshire.

Over time, the rulers of Dublin became increasingly Gaelicized. They began to exhibit a great deal of Gaelic and Norse cultural syncretism, and are often referred to as Norse-Gaels.

The extent of the kingdom varied, but in peaceful times it extended roughly as far as Wicklow (Wykinglo) in the south, Glen Ding near Blessington, Leixlip (Lax Hlaup) west of Dublin, and Skerries, Dublin (Skere) to the north. The "Fingal" area north of Dublin was named after the Norse who lived there.

In 988, Máel Sechnaill mac Domnaill led the initial Irish conquest of Dublin. As a result the founding of Dublin is counted by some from the year 988, notwithstanding that a village has existed on the site of Dublin since before the Roman occupation of Great Britain nearly a thousand years earlier. Máel Sechnaill mac Domnaill was dethroned by Brian Boru (1002–1014).

In the mid 11th century, the Kingdom of Leinster began exerting influence over Dublin, but its kings remained Norse-Gaels until the Norman invasion of 1171. Though the last Norse king of Dublin was killed by the Normans in 1171, the population of the city retained their distinctiveness based on their origins for some further generations.