The Battle of Mauropotamos was a battle fought in 844 between the armies of the Byzantine Empire

Byzantine Empire

The Byzantine Empire was the Eastern Roman Empire during the periods of Late Antiquity and the Middle Ages, centred on the capital of Constantinople. Known simply as the Roman Empire or Romania to its inhabitants and neighbours, the Empire was the direct continuation of the Ancient Roman State...

 and the Abbasid Caliphate at Mauropotamos in the theme of Optimaton (northern Bithynia

Bithynia

Bithynia was an ancient region, kingdom and Roman province in the northwest of Asia Minor, adjoining the Propontis, the Thracian Bosporus and the Euxine .-Description:...

). The battle followed a period of inconclusive warfare along the Cilicia

Cilicia

In antiquity, Cilicia was the south coastal region of Asia Minor, south of the central Anatolian plateau. It existed as a political entity from Hittite times into the Byzantine empire...

n marches and the loss of an entire Arab fleet off Cyprus

Cyprus

Cyprus , officially the Republic of Cyprus , is a Eurasian island country, member of the European Union, in the Eastern Mediterranean, east of Greece, south of Turkey, west of Syria and north of Egypt. It is the third largest island in the Mediterranean Sea.The earliest known human activity on the...

. The Byzantine regent, Theoktistos

Theoktistos

Theoktistos was an influential senior Byzantine official during the reigns of Michael II and his son Theophilos, and regent for the underage Michael III...

, resolved to end the impasse, but the battle resulted in a clear Abbasid victory, due to the desertion of some Byzantine officers. A civil war broke out among the Abbasids soon after however, and they were unable to exploit their victory. A six-year truce was consequently concluded in 845, followed by a prisoner exchange.