There are remains of an eighth- or ninth-century church at Ardagh, which is known as St. Mel's Cathedral, although it dates from three centuries after the saint's death, and predates the introduction of a diocesan system in Ireland.
A 9th-century church remains at Ardagh, known as St. Mel's Cathedral, despite being constructed during the lifetime of the saint by three centuries, and preceding the introduction of a diocesan administrative structure in Ireland.