No monument marks it. The precise location has never been established. What is known is that in the late summer of 1086, an army marching on Dublin was stopped here and decisively beaten, an event recorded in five separate sets of annals, those medieval Irish chronicles that serve as the primary written record of the period, yet one that has left no trace on the landscape.

The sequence of events that led to the battle began with the death of Tairdelbach Ua Briain, king of Munster and effective high king of Ireland, on 14 July 1086. His death, recorded in the Annals of Inisfallen, immediately destabilised the island's political order. Mael Sechniall, son of Conchobor Ua Mael Sechniall and king of Tara and Meath, seized the moment and marched south through Leinster with Dublin as his objective. The men of Dublin and Leinster mobilised quickly and met him at Clonliffe. The annals, including the Annals of Ulster, the Annals of Tigernach, the Chronicon Scotorum, and the Annals of Clonmacnoise, agree that his army was shattered. Mael Sechniall's forces included Mael Ciaran Ua Cathasaigh, king of Brega, and likely the king of Fir Chell, a territory corresponding to parts of modern County Westmeath and south-west County Offaly, along with warriors drawn from Clann Cholmáin and Síl nÁedo Sláine. Both allied kings were killed. Mael Sechniall himself survived, but his ambitions toward Dublin appear to have died with his army; he was killed in a separate conflict in north-west Meath the following year. The leaders of the victorious Dublin-Leinster side are not named in any surviving source. Whether Donnchad mac Domnaill Remair, king of Leinster at the time, was even present is unknown.

The Annals of the Four Masters, a seventeenth-century compilation and by scholarly consensus the least reliable of the annalistic sources, refer to the engagement as the 'Breach of Crinnach', a name that may point toward a pass or narrow defile on the approach to the city. According to Dr Gavin Hughes, whose summary informs this entry, the site may correspond to a place called Crinan, on the north bank of the Liffey near Clonliffe, and is thought to lie close to the boundary of the high medieval Liberty of Dublin, the formally defined zone of urban jurisdiction. The battle is thought to have been fought sometime in August or early September, though no annalist records an exact date. For anyone curious enough to look, the area around Clonliffe and the old Drumcondra approaches to Dublin offers a quiet kind of puzzle: ordinary streets laid over ground where, nearly a thousand years ago, a kingdom's ambitions ended without ceremony or commemoration.