Battle of the Plains
From Tolkien Gateway
A battle fought in III 1856, in which the armies of Gondor and their allies the Northmen faced the invading Wainriders. The battle was a disaster for Gondor; King Narmacil II was lost, as was Marhari the lord of the Northmen. After the battle, all of Gondor's eastern possessions fell under control of the Wainriders, who remained a constant threat for nearly another century.
