Between today's St Fillans and Dundurn lay the ruins of th historical St Fillans Chapel, whose Pre-Reformation ruins seem to date back to the 1300s, but whose origins might easily reach back into the late Pictish period. The shift to a lochside focus for settlement here seems to have happened in about 1250, when the MacNeishes built Loch Earn Castle on Neish Island, in the loch off St Fillans. By the 1400s the MacNeishes seem to have been making much of their living by preying off the property of their neighbours, and as early as 1490, James IV had tried to take action against them. At the battle of Glen Boltachan in 1522, Clan MacNab all but destroyed Clan MacNeish, the survivors only being saved by retreating to Loch Earn Castle. Matters finally came to a head in 1612, when some of the MacNeishes stole the Clan MacNab's Christmas supplies from a group of MacNabs on their way home from Crieff to their lands around Loch Tay.
The MacNabs responded by dragging one of their boats over the mountainous countryside between Loch Tay and Loch Earn, and, having arrived, rowing over to Loch Earn Castle and attacking the MacNeishes. As most of the MacNeishes were still enjoying the alcohol they had plundered from the MacNabs, and as they thought their possession of the only boat on Loch Earn made them invulnerable, the fight that followed was as once-sided as it was vicious. The MacNeishes were almost wiped out, and when the MacNabs later returned to Loch Tay it was without their boat, which they abandoned in Loch Earn, but with what was left of their Christmas supplies and with a number of MacNeish heads as trophies. Today, Neish Island can be seen in Loch Earn, off St Fillans, but little trace of Loch Earn Castle remains.