In his Historia Ecclesiastica (Ecclesiastical History of the English Nation, c. 731 AD) Bede noted that the Irish (Scots) and Britons had differed from the rest of the Western Church regarding Easter: “they did not keep Easter Sunday at the proper time, but from the fourteenth to the twentieth moon; which computation is contained in a revolution of eighty-four years”
This might suggest the Irish were at fault. Yet, for the past centuries and into the Carolingian Renaissance Irish scholars were at the forefront of “computus”, the development of the ecclesiastical calendar, most particularly the date of Easter. To do this correctly required observation of the moon, and facility at mathematics. “What Irish scholars of the seventh century achieved, therefore, was a comprehensive understanding of Easter reckoning, which was to become the unanimously accepted system for the calculation of Easter, from the ninth century onwards, for the rest of the Middle Ages and in the Orthodox Church to the present day”.