It is believed that the first monastery at Rahan was established by Camelacus in the 5th century under the direction of St Patrick, however this was almost erased from history during the early medieval period when it was assumed that St Carthach had been its founding father in 580AD, in fact he had simply refounded the site. St Carthach is also known in the annals as Mochuda and by the English as Carthage. It appears that St Carthach and 800 of his monks were expelled in 636 under the direction of King Blathmac, initially Carthach and his men refused to leave so by the drawing of lots a subordinate house of Killeigh monastery named Cluain Congusa was given the task of expelling Carthach and his men.

Monastic life returned in the 8th century when two brothers Fidhmuine and Fidairle ua Suanaigh refounded the monastery again. There is a 15th century reference to a Cornish King named Constantine who is said to have abandoned his throne to become a monk at Rahan, as mentioned in the Martryology of Oengus, but this could have dated from a time prior to the two brothers. Fidhmuine was an anchorite, a monk who lived a completely cut off existence. Monastic life flourished until the dissolution of the monasteries in the 16th century.

The earlier of the two churches that remain at Rahan, the whitewashed nave and chancel church, dates from the 12th century, originally it was built in the shape of a cross but these two transepts have largely disappeared. Its construction was started in the 12th century, the east window was inserted in the 13th century and further work on the vault and altar was carried out in the 15th century. The nave and other features were rebuilt in 1732, by the Church of Ireland, incorporating the earlier 15th century remnants. The Romanesque window and doorway are the real attraction of this church and this same design that is reflected in the second church, 100 yards to the east. An earlier church on this site was rebuilt in the 15th or 16th century and this is when the Romanesque doorway was inserted. The land all around these two wonderful churches is a patchwork of dividing lines and earthworks that display only an inkling of how bustling Rahan would have been during its illustrious life.

GPS: 53.27882, -7.6125