St Mary’s Cathedral was constructed with limestone in the mid-19th century using a cruciform design and an English Gothic style drawn by William Deane Butler. He was a founding member of the Royal Institute of Architect in Ireland. The church’s formal name is The Cathedral of the Assumption and Church of Saint Kieran. Ciarán of Saigir was a 6th century hermit who became a Bishop of Ossory and Ireland’s first native-born saint. This cathedral is the mother church for the Diocese of Ossory.