Crom Cruach or Cromm Crúaich, also known as Cenn Cruach or Cenncroithi, was a deity of pre-Christian Ireland, reputedly propitiated with human sacrifice, whose worship is said to have been ended by St.Patrick.
Crom Cruach's name takes several forms and can be interpreted in several ways. Crom (or cromm) means "bent, crooked, stooped". Cenn means "head". Cruach can be an adjective, "bloody, gory", or a noun, meaning variously "slaughter", "stack of corn", or "pile, heap, mound". Plausible meanings include "bloody crooked one", "crooked stack of corn", "crooked one of the mound", "bloody head", "head of the stack of corn" or "head of the mound". It has also been interpreted as deriving from Proto-Celtic *Croucacrumbas "crooked one of the tumulus.
The references in the dinsenchas to sacrifice in exchange for milk and grain suggest that Crom was a fertility deity. The description of his image as a gold figure surrounded by twelve stone or bronze figures has been interpreted by some as representing the sun surrounded by the signs of the zodiac, making Crom a solar deity.
He may be related to the later mythological and folkloric figure Crom Dubh.
According to an Irish dinsenchas ("place-lore") poem in the 12th century Book of Leinster, Crom Cruach's cult image, consisting of a gold figure surrounded by twelve stone figures, stood on Magh Slécht ("the plain of prostration") in County Cavan, and was propitiated with first-born sacrifice in exchange for good yields of milk and grain. Crom is said to have been worshipped since the time of Eremon. An early High King, Tigernmas, along with three quarters of his army, is said to have died while worshipping Crom on Samhain eve, but worship continued until the cult image was destroyed by St. Patrick with a sledgehammer.
This incident figures prominently in medieval legends about St. Patrick, although it does not appear in his own writings, nor in the two 7th century biographies by Muirchu and Tírechán. In the 9th century Tripartite Life of Saint Patrick the deity is called Cenn Cruach, and his cult image consists of a central figure covered with gold and silver, surrounded by twelve bronze figures. When Patrick approaches it he raises his crozier, the central figure falls face-down, with the imprint of the crozier left in it, and the surrounding figures sink into the earth. The "demon" who inhabits the image appears, but Patrick curses him and casts him to hell. Jocelin's 12th centure Life and Acts of St. Patrick tells much the same story. Here the god is called Cenncroithi, interpreted as "the head of all gods", and when his image falls the silver and gold covering it crumble to dust, with the imprint of the crozier left on bare stone.
A decorated stone which has been interpreted by some as the cult image of Crom Cruach was found at Killycluggin, County Cavan, in 1921. Roughly dome-shaped and covered in Iron Age La Tène designs, it was discovered broken in several pieces and partly buried close to a Bronze Age stone circle, inside which it probably once stood. The site has several associations with St. Patrick. Nearby is Tobar Padraig (St. Patrick's Well), and Kilnavert Church, which is said to have been founded by the saint. Kilnavert was originally called Fossa Slécht or Rath Slécht, from which the wider Magh Slécht area was named.
Although now much damaged, the stone can be reconstructed from the different surviving pieces. At the base of the stone there were four rectangular adjoining panels measuring 90 cm each in width giving a circumference of 3m 60 cm when it was first carved. The height of each panel was about 75 cm. When excavated and placed upright on its flat base, it was found to lean obliquely to the left from the vertical, perhaps explaining the name Crom, "bent, crooked". The Killycluggin Stone, as it is known, is now in the Cavan County Museum, while a replica stands near the road about 300 metres from the original site.
The 14th century Book of McGovern, written in Magh Slécht, contains a poem which states that Crom was situated at Kilnavert beside the road and that the local women used to tremble in fear as they passed by. There is still a local tradition in the area that the Killycluggin stone is the Crom stone.
There is another standing stone identified with Crom Crúaich in Drumcoo townland, County Fermanagh. A nearby street is named Crom Crúaich Way after it. It has the figure of a man walking engraved on it which either represents Saint Patrick or a druid, depending on when it was engraved.