On October 15, 1211, the Battle of the Rhyndacus was fought between the main successor states of the Byzantine Empire, the Latin Empire and the Byzantine Greek Empire of Nicaea, established following the dissolution of the Byzantine state after the Fourth Crusade.
Henry of Flanders, the second emperor of the Latin Empire of Constantinople, wanted to expand his territory in Asia Minor at the expense of the Nicaeans.
He had already achieved a victory in 1205, occupying the city of Adramyttium and using it as a base to attack the Byzantines.
Taking advantage of the losses suffered by the Nicaean army against the medieval Turko-Persian Empire of Seljuks in Antioch’s clash (1211), Henry approached with his army the Rhyndacus river.
Henry with not more than 260 Frankish knights, had to face an ambush prepared by the enemy. He attacked Nicaean troops and their positions and scattered them during a day-long battle on 15 October.
After the battle Henry marched unchallenged through Nicaean territories and reached south as far as Nymphaion.
Later, the both sides concluded the Treaty of Nymphaeum, a peace treaty signed in December of 1214 between the Nicaean Empire, successor state of the Byzantine Empire, and the Latin Empire, which was established in the aftermath of the Fourth Crusade of 1204.