The river Isen (SindarinAngren) was not crossable anywhere south of its origin in Isengard, except at the Fords of Isen which were just above the point where the Isen bent west towards Belegaer. As it was the only way into Gondor and later Rohan, it was closely guarded from the fortresses of Isengard and the Hornburg at Helm's Deep.
During the War of the Ring the fords were attacked from both shores by Orcs of Saruman who had passed south from Isengard in secret, and King Théoden of Rohan's son Théodred was killed when Gríma Wormtongue refused to send reinforcements. Despite Théodred's death a company of the Rohirrim under Grimbold attempted to hold the fords, but they had to give them up against a force which outnumbered them more than five times.
The surviving Rohirrim fled south to the Hornburg, just nearly outrunning Saruman's forces, and almost doubled the number of defenders during the Battle of the Hornburg.
The battle was fought on November 3, 3019, in the village of Bywater.
Battle between the forces of the Witch-king of Angmar and the combined forces of the Dunedain of the North, Elves of Lindon and Rivendell, and Men of Gondor.
The Orcs in the valley regrouped and rejoined the battle.
Tolkien's fictional universe of Middle-earth, the Fords of Isen were fords in the river Isen, guarded by the Rohirrim.
During the War of the Ring there were two battles at the Fords of Isen.
The first battle took place on February 23rd, 3019 T.A. The second was on March 2nd, T.A. The battles were between Saruman's Uruk-hai and the Rohirrim of Rohan.