On Easter Monday in 1209, a large number of the Anglo-Norman citizens of Dublin ventured out of the walls to play a hurling match on the flat land at Cullenswood (beside the modern Sandford Road in Ranelagh today) which was customary on Easter Monday.
There, they were attacked unawares by the local Irish septs of the neighbouring mountains (probably led by the O’Byrne and O’Toole families) who saw their opportunity to descend on the unaware citizens. In this bloody and savage attack, about 500 people were massacred and the remainder driven into the town.
- Cullen's Wood was variously spelt Colonia, Cullen, Colyn, Cullyn and Colon, with a number of references to the "Wood of Cullen" In The Calendar of Archbishop Alen's Register, c. 1172-1534.
The day was for a long time after distinguished by the name of Black Monday, and commemorated by a parade of the citizens on the field of the conflict, were they appeared in arms and challenged their enemies to renew the encounter.