At the famous Battle of Glenmalure in 1580, an Irish Catholic force made up of Gaelic clans from the Wicklow Mountains, led by Fiach McHugh O'Byrne, defeated an English army under Lord Grey. The fighting took place at the O'Byrne mountain stronghold in Glenmalure. 

While trying to climb the steep slopes of the valley, the inexperienced English soldiers were ambushed by the Irish rebels, who had hidden themselves in the woods. The English army of 3,000 suffered 800 casualties. However, when offered terms a year later, O'Byrne surrendered to the English administration.