Magh Slécht (pronounced Moy Slett) is the name of an historic plain in Ireland. It comprises an area of about three square miles (8 km²) situate in the south-eastern part of the Parish of Templeport, Barony of Tullyhaw and County of Cavan. It is bounded on the north by Templeport Lough, on the east by Slieve Russell mountain, on the south by the Woodford Canal & on the west by the Blackwater River. It was originally named Magh Senaig (the plain of the hill-slope) but the name was later changed to Magh Slécht (The plain of prostrations) as it became the nationwide centre of the cult of the god Crom Cruaich. The ancient Irish prayed by prostrating themselves in a similar fashion to today's Muslims, ie by kneeling down on both knees and touching the forehead against the earth. The plain is not flat but consists of little drumlin hills. However as it is surrounded by mountains it is a plain in comparison.

This area has been in constant occupation from pre-4000 B.C. up to the present day, as is evidenced by the huge number of ancient monuments which still survive. In a small area of 3 square miles (8 km²) there are over 80 monuments of different types, with many others bound to be discovered by future archaeological searches. It is the densest grouping of such monuments in County Cavan and possibly in Ireland. Included are 9 megalithic tombs, 7 Ring-Barrows, 3 different stone-circles, 9 different standing-stones, 2 stone-rows, 5 enclosures, 6 crannogs, 33 raths or souterrains, 3 Early-Christian church-sites, 2 Early-Christian Holy Wells, 2 Bullauns & 2 Medieval castles.

The area was first inhabited by Neolithic hunter-gatherers who arrived via the river (originally called the Gráinne River & now canalised as the Woodford Canal or the Shannon-Erne Waterway). The first named inhabitants were the Masraighe tribe who ruled Magh Slécht until they were conquered by the Ui Briuin tribe in the 8th century A.D. The Masraighe were also called the sons of the Liath or the Tuatha Slécht and Magh Slécht was sometimes called Liathmhuine. The descendants of the Ui Briuin are now called the McGovern clan and are still the most numerous surname in the area. Magh Slécht formed part of the Province of Connacht until the 16th century when it was made part of the Province of Ulster.

The main events in the history of Magh Slécht as listed in the ancient sources are (1)The death of the High-King of Ireland, Tighernmas & his followers in the Seventh Plague of Ireland while worshipping Crom Cruaich on 31st October(Samhain, Halloween), 1461 B.C. His grave is marked by a standing stone(2) The murder of the Ulster hero Conall Cernach in the 1st century B.C at Ath na Mianna (Ballyconnell). His grave is supposedly marked by a hilltop cairn (3)The destruction of the idol Crom Cruaich(Probably the phallic La Tène Killycluggin Stone)by St.Patrick in the 5th century A.D. and the founding of a church there at Fossa Slécht under St.Methbrain. (4)The murder of King Conall Gulban of Donegal by the Masraighe in 464 A.D. (5)The birth of St.Mogue (also known as St.Aidan of Ferns) in 550 A.D. (6)The foundation of the University of Tuaim Drecain(Tomregan) by the Synod of Drumceat in 584 A.D. (7)The murder of the relatives of Baetan in 621 A.D. (8)The Battle of Magh Slécht in 1256 A.D.