The Mairtine (Martini, Marthene, Muirtine, Maidirdine, Mhairtine) were an important people of late prehistoric Munster, Ireland who by early historical times appear to have completely vanished from the Irish political landscape. They are notable for their former capital, Medón Mairtine, becoming the chief church of the later Eóganachta, namely Emly.
Geoffrey Keating's History of Ireland includes the following section, which may refer to the eponymous ancestor:
"Eochaidh Apthach (Eochu Apthach) son of Fionn, son of Oilill, son of Flann Ruadh, son of Rothlan, son of Mairtine, son of Sithcheann, son of Riaghlan, son of Eoinbhric son of Lughaidh, son of Ioth, son of Breoghan (Breogán), held the sovereignty of Ireland one year; and he was called Eochaidh Apthach because of the number who died in Ireland in his time; for the plague or other disease seized upon the men of Ireland each month, from which many of them died; hence the name Eochaidh Apthach clung to him; for apthach means 'fatal'; and he himself fell by Fionn son of Bratha."
This would make Mairtine mac Sithcheann a gr-gr-gr-gr-grandson of Breogán mac Brath, mythical king of Galicia. Breogan's grandson, Míl Espáine, was the father and uncle of the first Goidelic people to settle in Ireland.
Eochu Apthach, Mairtine's gr-gr-gr-grandson, is given as a member of the Corcu Loígde. His reign is variously given as the 6th/5th, 7th, or 8th, century BC.
However, it is nowhere explicitly stated that Mairtine mac Sithcheann was the eponym of the Mairtine people. Plus, the Mairtine people are accorded status of Fir Bolg, who were predecessors of the Gaels.
This term has been translated as middle of the Mairtine [nation], indicating that modern-day Emly, County Tipperary, was the central capital of the tribe. It is due west of Tipperary town, which is due west of Cashel, seat of the historic kings of Munster. It is therefore at what can be roughly regarded as the geographic centre (or middle, medón) of Munster.