Capstone – The large stone which sits on the portal stones and side stones of a portal dolmen (see portal dolmen)
Chancel - East end of the church in which the altar is placed.
Cillin - Burual ground for unbaptised children.
Cist burial - Found underground with a stone base, sides and top. Can be found near standing stones and often have a covering barrow or cairn. Neolithic/Bronze Age.
Cross slabs – Cross slabs are early Christian slabs of stone on which a crucifix has been carved. These were later replaced by high crosses. They usually date from the 6th to 9th centuries.
Crypt - An underground chamber in a church.
Cup Marks - Circular shapes found in rock art called cup marks because they look like a cup ring.
Cup mark on the Clonfinlough Stone in Co. Offaly.
Curtain wall - Similar to a bawn (associated with towers houses and fortified houses). An encompassing defensive wall around a medieval castle and grounds.