Robert De Muscegros, a Norman, built the first defensive fortress (an earthen mound with a strong wooden tower on top) in 1250.
His lands were later granted to Thomas De Clare who built the first stone castle on the site. About this time Bunratty became a large town of 1,000 inhabitants.
In 1318 Richard De Clare, son of Thomas was killed in a battle between the Irish and the Normans. His followers were routed and the castle and town were completely destroyed. The castle was restored for the King of England but was laid waste in 1332 by the Irish Chieftains of Thomond under the O'Briens and MacNamaras. It lay in ruins for 21 years until it was rebuilt by Sir Thomas Rokeby but was once again attacked by the Irish and the castle remained in Irish hands thereafter.