According to legend, Duncannon dates back to the time of Fionn Mac Cool and the Fianna in the 3rd century. Duncannon was of strategic importance on the vital sea penetration of Waterford Harbour. It was greatly involved in wars and sieges for almost 17 centuries. Leaders and kings have landed on and fled its portals, armies have struggled, and Napoleon sought and got intelligence from its strength and weakness. It is still used as a modest Irish army post, mainly for summer training. It has a sandy beach with fishing and pleasing amenities, which makes it a very popular resort.