Christianity reached Kincardine O'Neil late in the 5th Century with the establishment of a church by St. Erchard (disciple of St Ternan), St. Erchard is now the patron saint of Kincardine O'Neil. A well was erected in his honour on the edge of the village. St Erchard's day is the 24th of August. It seems likely that this early Celtic Church was on the same site as the later 13th Century ruin of St. Mary's church. The Celtic Church existed in Kincardine O'Neil from the year 496 but the distinctive pattern of worship changed to come in line with Roman Catholicism in the time of Malcolm III in the 11th Century (see below). Turbulent times followed the Reformation but by 1690 the establishment of the reformed Presbyterian Church of Scotland meant that St. Mary's had severed its connection with the Roman Catholic church. Owing to its location Kincardine O'Neil has been involved in a number of historic events.