Callan was founded by William the Marshall in 1207 and reputedly gets its name from the High King of Ireland, Niall Caille. It is reported that while at war with the Vikings the High King arrived in Callan to find that its river was in flood. The King witnessed his servant trying to cross the river and being swept away by the fast flowing current. The King, recorded in history as a man of action, seeing the impending disaster, impetuously urged his horse into the fast flowing river in a vain bid to save his servant, only to be also overcome and drowned by the torrent. The river in question is now named the "Kings River".