It is believed that Aghadoe, a village that overlooks Killarney townland and Mountains, may have originated as a Pagan Religious Site. The area has also been linked with 5th century missionaries; however the first major discovery that Aghadoe was an important site was the discovery of the 7th Century Ogham Stones. According to the Annals of Innisfallen, St. Finian the Leper founded another monastery at Aghadoe around the 6th or 7th century, dating from 939; the monastery is also known as the “Old Abbey”. Also present in the vicinity is the 13th century Parkavonear Castle, built by the Normans in 1169 post the Anglo-Norman Invasion.
It is believed that the monastery on Innisfallen Island is closely linked with the monastery at Aghadoe; reference is first made to their relationship in the Annals of Innisfallen while also a great scholar of Innisfallen was buried in Aghadoe in 1010 AD. The round tower began construction in 1027; with the 12th century came new rulers, Eóganacht Locha Léin, who constructed a new church in Romanesque style called the ‘Great Church’. The church was finally completed by the end of the 12th century with the addition of a chancel; this was later segregated from the rest of the church by a wall.
Two ogham stones were discovered on site; these findings suggest how important the site was dating from the mid-7th century. One stone remains cemented into the south wall of the chancel while the other went missing. Another artefact called a ‘Ballaun’ can be found outside on the north-west corner of the church; it was used to gather holy water and was also believed to have brought great healing powers.