The event is not told of in the works that mention the greater Battle of the Last Alliance, part of which took place at Dagorlad, during the preceding Age.
The battle was precipitated by a warning from the Éothéod Lord Marhwini to King Calimehtar that the Wainriders were again about to attack Gondor once again. Their plan was to attack the Gondor province of Calenardhon from the across the Undeeps and that a full scale rebellion in Rhovanion was in preparation. Calimehtar assembled his army and Marhwini prepared a éored.
Calimehtar led his army up through Ithilien openly ensuring the enemy would know their intent. Seeing this, the Wainriders committed all they had in a great force to meet them, then Calimehtar turned away which led them west into Dagorlad further from their conquests in Rhovanion, and there a great battle began. During the long struggle, Calimehtar sent cavalry over the Undeeps which were unguarded by the enemy due to them sending everything against Calimehtar's main host. Here, they joined up with Marhwini's éored and attacked the enemy from the rear sealing their doom. Gondor was victorious. The Wainriders scattered in disarray.
Though Gondor won, Calimehtar did not pursue them to the death for the most part but Marhwini's cavalry continued to harass the survivors near southern Mirkwood, humiliating and taunting them at all at the harm they had done to the innocents of Rhovanion. Soon afterwards, the Northmen would rebel against their cruel overlords and be free of them.