St. Celsus of Armagh, a Benedictine monk, was born in Ireland in 1079. He is said to have been the last hereditary archbishop of Armagh in Ireland. He taught in Oxford, England. He traveled across Ireland to preach and reform. In 1111, he helped preside at a synod that helped align the Irish church with the rest of Europe. St. Celsus also brokered peace among kings and chieftans in Ireland. He died in 1129.