Fachtna of Rosscarbery came to the area in the late sixth century and founded a monastic site.

[3] This had been the principal monastery of West Cork; Brendan the Navigator taught there, and it was a school for international students in its time.

[citation needed] The ruins of a church erected by St Faughnan [sic] still exist on the southern slope of the land on which Rosscarbery is built.

[4] A church or cathedral has occupied the site since at least the tenth century,[5] and after Bishop John Edmund de Courcy resigned in 1517, Pope Leo X ordered an inquiry into the state of the diocese, and it was noted that by then a cathedral stood on the site.

The former house of Bishop Lyon (who had died in 1617) was burnt down, and his deaf and dumb daughter perished in the fire.

[6] St Fachtna's is the smallest cathedral in Ireland, being the size of a typical parish church.

Peter Galloway described the building, as "an odd collection of architectural bits and pieces", noting that it incorporates only a little medieval work, while the mixture of Gothic and Georgian windows along with wooden casements with stone linteled heads leave the cathedral with a confusing architectural style.