An Cathach (meaning ‘the Battler’) was a very important relic used by the Clan Ó Domhnaill (O’Donnell Clan), the old Gaelic royal family in Tír Chonaill (mainly modern County Donegal) in the west of Ulster. It was used as a rallying cry and protector in battle. It was said to protect and guarantee victory in war to the Donegal leaders. Before a battle it was customary for a chosen monk/holy man (usually attached to the McGroarty clan, and someone who was sinless) to wear the Cathach in its cumdach around his neck and then walk three times around the troops of O’Donnell. It is the oldest surviving manuscript in Ireland, and the second oldest Latin psalter in the world. The name of the book derives from the Irish Gaelic word cath (pronounced KAH) meaning ‘battle’. An Cathach means ‘the battler’. The hereditary protectors/keepers of An Cathach were the Mag Robhartaigh/McGroarty clan from Ballintra in south Donegal. An Cathach, the Battler, has been dated to around the period 590 to 600 AD. The decoration throughout An Cathach is limited to the initial letters of each psalm. An Cathach is now housed in the Royal Irish Academy (entrusted to them in 1842).