Ireland · Partial ruin
O'Brien's Castle
Caisleán Uí Bhriain
O'Brien's Castle (Furmina Castle) is an early 15th-century rectangular tower house on Inisheer, built by a branch of the O'Brien family. The donjon contains vaulted ground-floor storage chambers, a first-floor great hall and mural stairs up to a parapet with a corbelled bartizan. The structure stands on one of the island's highest points and today survives as a partial ruin.
Its prime
1400
Today
Partial ruin
As it stood in 1400
What O'Brien's Castle looked like in its prime.
A rectangular stone donjon/keep of grey limestone rubble with squared ashlar quoins at the corners, rising directly from a grassy island ridge. Tall, straight walls punctured by narrow slit windows and a small ground-level storage doorway, with a first-floor entrance originally reached by an external timber stair. A parapet and crenellated walk with a projecting bartizan (its corbel carved with a human face) crowns the tower in its complete state.
Its story
The story of O'Brien's Castle.
Dún Formna and the Clann Teige Tower, c. 1400
The high ground in the north of Inisheer carried a ringfort long before any tower house: Dún Formna, the "hillfort of the ridge/shoulder", named for the shoulder of land it stands on and dated to between the 5th century BC and the 1st century AD. On that site the Clann Teige, a branch of the O'Brien (Uí Briain) family, built the castle in the early 15th century, around 1400, at one of the island's highest points. It is also called Furmina Castle.
Taken by the O'Flahertys c. 1582, Slighted in 1652
The castle was taken by the Ó Flaithbheartaigh, the O'Flahertys, around 1582. It was captured and slighted by Oliver Cromwell's army in 1652, during the Cromwellian conquest of Ireland.
A Donjon Entered at the First Floor
The castle is a rectangular donjon, or keep, whose original doorway opened not at ground level but into the first floor, reached by an external wooden stairs. That first floor was given over entirely to a great hall, with mural stairs running up within the wall to the parapet, while the ground floor was a basement or storage area of three vaulted chambers. The corbel of a bartizan is visible, with a human face carved into it. The tower house is a National Monument.
Step inside
8 places to explore in 1400.
The record describes 8 distinct spots at O'Brien's Castle, including 3 interiors: first-floor great hall, mural stairs within the wall, ground-floor vaulted chambers. Create your own photoreal reconstruction and explore every one, more scenes means more rooms, more angles, and more of the place to stand in.
Build Your Own Castle
Recreate O'Brien's Castle with AI to explore it.
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Clans who held O'Brien's Castle.
The families that held O'Brien's Castle for a decade or more across its history, follow a name to its clan.
Built around 1400 by the Clann Teige, a branch of the O'Briens (Uí Briain).
