The Latin emperor, Henry of Flanders, desired to expand his territory in Asia Minor at the expense of the Nicaeans.

He had already achieved a victory in 1205 at Adramyttium, but the need to counter the Bulgarians in Europe had forced him to conclude a truce and depart.

Laskaris prepared an ambush at the Rhyndacus, but Henry assaulted his positions and scattered the Nicaean troops in a day-long battle on 15 October.

The Latin victory, won reportedly without casualties, was crushing: after the battle Henry marched unopposed through Nicaean lands, reaching south as far as Nymphaion.

Warfare lapsed thereafter, and both sides concluded the Treaty of Nymphaeum, which gave the Latin Empire control of most of Mysia up to the village of Kalamos (modern Gelenbe), which was to be uninhabited and mark the boundary between the two states.