The Wainriders were beginning to recover themselves from their defeat at Dagorland and were apparently not completely driven out by the rebellion in Rhovanion, and now had new allies from Khand and Harad. The new Éothéod lord, Forthwini found out about this and warned King Ondoher of it. Meanwhile, Eärnil, based at Pelargir received this news on the ninth day of Cermië and prepared a force that crossed the river Anduin in part, leaving the Fords of the Poros purposely undefended.
Eärnil's southern army camped forty miles north in South Ithilien apparently waiting to face the enemy from the south or to support the forces led by his king in the north. Unfortunately, things went ill for the king at the Black Gate leading to the death of him and his son. Now Eärnil would face an army of Haradrim.
The Haradrim crossed the Poros and Eärnil met them. Eärnil utterly defeated them destroying the entire army. Little to no details are known about the battle itself save that the Haradrim army was completely destroyed, and Eärnil's losses were apparently light.
After Eärnil's victory, he and his army moved north to assail the Wainriders, who believing they were now victorious over Gondor were busy feasting and celebrating in their camps. Here, Eärnil would defeat them once and for all.