The Snakes in Ireland were the Druid, the Celt, and the Saxon who would not capitulate to The Vatican, and The Holy Roman Empire.
The Holy Roman Empire sent a “Monk-Knight” named Patrick, with a small contingent of Monk-Knights to do the bidding of The Vatican.
They wiped out the people who would not capitulate to The God, and Pope of the Holy Roman Empire. 
They Genocided them, and drove the survivors north.
Patrick did such a good job?
They made him a saint!