Ally of the O'Reillys, Walter de Burgh, raided deep into Connacht and devastated the O'Conors. According to the Annals of Connacht, de Burgh had an army of 20,000 men, but this is most definitely exaggerated. This was followed by an O'Reilly attack in western Breifne (modern County Leitrim), the home territory of the O'Rourkes. The two armies were meant to rendezvous at Lough Allen but the O'Reillys came under heavy attack and retreated. They were pursued by Aedh O'Conor and his cavalry to Magh Slecht, where the battle ensued.