O’Brien’s Castle is proudly located on the highest point of the island. This castle is thought to have been built in 14th century making it the oldest ruin on Inisheer. It would pre-date the other ruins in surrounding areas of County Clare such as the Burren Tower Houses and other stone forts on the Aran Islands.
The early Tribal Kingdoms that divided Ireland often competed for resources and were not exactly known for their peace making. It is not surprising that in 1582 the O’Flaherty’s of Connemara sieged and occupied the castle from the ruling O’Brien’s of Munster. The O’Flaherty family was driven west due to the invasion of Norman conquerors but fought ferociously to maintain their influence in the area. To this day many decedents of the O’Flaherty’s still reside on the Aran Islands. Years later in 1652 the Aran Islands were given up to Cromwellian forces and the O’Flaherty’s defeated. Unfortunately, O’Brien’s Castle was taken yet again and this time partially destroyed. The new forces favoured other Island strongholds such as the ring forts of Inis Mór, leaving the Castle to sadly fall into ruin to this very day.