Black Monday, Dublin, 1209 – when a group of 500 recently arrived settlers from Bristol were massacred by warriors of the Gaelic O'Byrne clan. The group had left the safety of the walled city of Dublin to celebrate Easter Monday near a wood at Ranelagh, when they were attacked without warning. For centuries afterwards, this event was commemorated by a mustering of soldiers on the day as a challenge to the native tribes.
Black Monday, 14 April1360 – the army of Edward III during the Hundred Years' War was struck by hailstorms, lightning and panic, causing considerable loss of life on Easter Monday.