O'Brien's Castle

O’Brien’s Castle

Tour Stop : Yes

Last Updated : 18 January 2023

O'Brien's Castle, Inisheer, County Galway

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O’Brien’s Castle, located on the high point of the island, dates back to the 14th century. The castle was besieged by the O’Flahertys of Connemara in 1582 who were driven west by the Norman conquest but fought fiercely for their local influence. Years later it was taken again by English Cromwellian forces and partially destroyed in favour of other strongholds and ring forts on Inis Mór. Today visitors taking the ferry from Doolin to Inis Oírr see this magnificent ruin first, overlooking the beaches and pier below, when they arrive.

The Castle sits on top of the hill of the smallest Aran Island, Inis Oírr. Although O’Brien’s is in ruins, and has been for centuries, it still stands proudly as a reminder of the island’s history and heritage. Dating back to around 1400 O’Brien’s Castle has, for many centuries, been the largest structure on the island, dominating its surroundings. Despite its decay, O’Brien’s remains an impressive sight; visitors can wander through the crumbling towers whose thick walls are still intact. The hill offers spectacular views of Inis Oírr, Inis Mór, the Clare coast and the Cliffs of Moher.


The History of O’Brien’s Castle

Before the castle, the earthworks of Dún Formna stood on the shoulder-shaped hill. This fortification, or ringfort, is thought to have been built between 600 DC and 100 AD. Its name meaning “hillfort of the ridge/shoulder” is evidence that there has been a powerful symbol in this site since the pre-Christian period. Constructed by a branch of the O’Brien family, Clann Teige, in the early 1400s, the castle was then seized by the Ó Flaithbheartaigh (O’Flahertys) around 1582.

Oliver Cromwell’s army captured and slighted the O’Brien’s Castle in 1652 during the invasion and occupation of Ireland in this period. Slighting is an act of destruction, typically done to high-status buildings to deprive them of their military and strategic value. This practice not only included the building but also its content as well as the surrounding area, especially farmland. The castle has been a ruin, and unoccupied ever since.

Described as a “grand spectacle,” O’Brien’s Castle takes the shape of a rectangular Norman “donjon,” or keep. The original entranceway would have been accessed via an external wooden stairwell, leading to its first floor. The entire first floor is a great hall. Here, mural stairs would spiral towards the parapet, while beneath an expansive basement with three vaulted chambers. An impressive bartizan (overhanging, wall-mounted turret) is still visible today and bears upon it an intricately carved human face.

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O'Brien Arms, O'Brien Castle

The O’Brien’s

The O’Brien dynasty (Ua Briain in Classical Irish), a noble house of Munster, was founded in the 10th century by Brian Boru, widely regarded as the most successful and unifying kings of the mediaeval period in Ireland. He shortly after became King of Munster, and through conquest he

established himself as High King of Ireland, or Ard Rí na hÉireann. Boru descendants, who carried the name Ó Briain, ruled the Kingdom of Munster until the 1100’s. Over this period rivals took pieces of territory, but they would hold the Kingdom of Thomond for just under five hundred years.

The O’Flaherty Clan

O’Flaherty is an Irish Gaelic clan prominently located in what is today County Galway. They took O’Brien’s Castle in 1582. The clan name originated in the 10th century, derivative from its founder Flaithbheartach mac Eimhin. Originally they were kings of Maigh Seóla, today an area around lock Corib. In the 11th century the family were pushed further west to Iar Connacht, roughly Connemara today. They ruled this territory until the 1500s. The name has been translated into English in a number of ways, including Flaherty, Faherty, Laverty, Flaverty, Lahiff, and Flahive.


O’Brien’s Castle is a must for every tourist visiting Inis Oírr, even just for the view of the island and the coast in the distance. Its history tells the story of Inis Oírr, the Aran Islands and of Connacht. Wanderly Wagon stops there 3 times (or more) each and every day between April and October.

O’Brien’s Castle Image Gallery