There is no marker, no monument, and no clearly defined field to visit. The battlefield, if it can be called a single place at all, may have stretched over a considerable distance as de Clare's mounted knights pursued the fleeing Connacht forces until evening. That pursuit, as much as any single clash of arms, was the battle.

The engagement came at the end of a two-month siege. Ruaidrí Ua Conchobair, high king of Ireland, had assembled a coalition of provincial lords and kings following the death of Diarmait Mac Murchada, king of Leinster, in May 1171. His forces encircled Dublin in a series of camps: Mac Duinn Shléibe at Clontarf, Ua Brian, king of Munster, at Kilmainham, Muirchertach at Dalkey, and Ua Conchobair himself at Castleknock. Guthred of the Isle of Man contributed around 30 ships to blockade the Liffey. Food inside the city was growing scarce. Peace talks reportedly collapsed when Ua Conchobair offered the Anglo-Normans only the three Hiberno-Scandinavian towns of Dublin, Waterford, and Wexford. Richard de Clare, known as Strongbow, the earl of Pembroke, then commanding the garrison alongside Myles de Cogan and Raymond Le Gros, chose attack over attrition. His force, probably fewer than 1,000 men, mustered around 4pm, feinted towards Finglas, then looped back eastwards on Castleknock, possibly using the Tolka valley as cover. Both the Song of Dermot and the Earl and Giraldus Cambrensis record that the Irish were taken completely unawares, some of them bathing. The Annals of Tigernach offer a cooler account, suggesting Ua Conchobair and his cavalry were elsewhere when the camp was struck, and that those killed were largely camp followers rather than fighting men. Whatever the reality, the other siege camps collapsed immediately and Ua Conchobair's army withdrew. Casualty figures in the sources range widely, with the highest estimate placing the dead at 1,500.

Because the battlefield has no fixed or agreed location and no dedicated access point, a visit is really an exercise in landscape reading. The area between Castleknock village and the Tolka valley to the north is the relevant ground, and the topography, low ridges, a river valley used for concealment, still makes the tactical logic of de Clare's approach legible. The battle is one of three fought around Dublin between 1170 and 1171, the others being the battle of Dublin and the battle of Hoggen Green, and considering the three together gives a clearer sense of how quickly and contingently the Anglo-Norman grip on the city was established. The primary sources, the Song of Dermot and the Earl, Cambrensis' Expugnatio Hibernica, and the Annals of Tigernach, disagree on almost every particular except the outcome.