Clonmacnoise (Irish: Cluain Mhic Nóis, “meadow of the sons of Nos”) is a monastic site overlooking the River Shannon in County Offaly. Among its ruins there is a cathedral, a castle, two round towers, numerous churches, two important high crosses, and a large collection of early Christian grave slabs.

The monastery settlement was founded in 548 by St. Ciaran, the son of a master craftsman. It soon became a major center of religion, learning, trade, craftsmanship and politics, particularly because of its central situation in Ireland.

Clonmacnoise achieved its fame as a centre of religion, but there was also a considerable number of lay people in residence there. The earliest churches at Clonmacnoise were made of wood, but from the 10th century onward they were built of stone.