SMR No.: OF005-004001-
Monument Type: Cathedral
The cathedral was the main church of the monastic settlement and along with Temple Ciarán is the earliest stone building on the site. The Irish annals record that it was built by Flann Sinna, king of Ireland and Colmán, abbot of Clonmacnoise in AD909. It is a rectangular church built with roughly coursed rubble with four distinct building phases evident. The earliest 10th/11th-century phase is indicated by the presence of antae at both ends of the church. The next phase appears in the 13th century with the insertion of the W doorway with four orders and the sacristy or chapter house which was added to the E end of the S wall. The sacristy/chapter house which is marked as 'Black Cell' on Blaymire's map 1738 is lit by two single light round headed windows set in widely splayed embrasures. The doorway from the sacristy/chapter house to the church has a pointed arch with concave hood moulding above with diagonal stone tooled jambs indicating early medieval date. In the late 13th/14th-century the S wall was moved northwards with the insertion of a single light gothic style lancet, the rear arch of which still survives at the E end of the S wall. The sacristy/chapter house was extended northwards with the insertion of the double sedilia in the S wall.
The fourth and final phase was in the mid 15th-century when a simple twin light tracery window was inserted into the S wall at the E end replacing the lancet light. During this phase the rib vaulting was inserted at the E end of the church along with the insertion of the N doorway. The pointed limestone door at the W end of the N wall known as Dean Odo's door is in the perpendicular gothic style and is finely decorated with dragons, angels and ogee headed panels. There are three saints carved over the door representing St. Dominick, St Patrick and St. Francis. The sacristy/chapter house had a second floor inserted over the ground floor possibly in the 15th-century with a fireplace and octagonal chimney stack with funnel shaped cap.