Catalan campaign in Asia Minor

In 1303, the Byzantine Emperor Andronicus II Palaeologus hired 6,500 Catalan mercenaries under Roger de Flor to campaign against the Turks in the spring and summer of the same year. Their costly service came with success, driving back the Turks in parts of Asia Minor. At Philadelphia, 18,000 Turkish soldiers (possibly those of Aydinids) were left dead, the work of the Catalans.

However, the Byzantines got more than what they bargained for; the mercenaries were difficult to restrain and consequently much of the reconquered territory was laid to waste. When their leader Roger de Flor was assassinated in Gallipoli on 3 April 1305 by Michael IX Palaeologus followed by a massacre of 1,300 Catalans, the mercenaries began a two-year pillage in revenge and crossed over to Thrace and Macedonia under the command of their new leader, Berenguer d'Entença, where further raiding occurred. As a result of this brutality, the Company was excommunicated by Pope Clement V. Eventually the Catalan mercenaries claimed the Duchy of Athens for themselves in 1311 and would remain there until 1379, leaving behind a devastated Byzantium. After this, the Turks found much support amongst those who suffered and reoccupied land that had been lost.

Thus, the Catalans' campaign was a short-term Byzantine victory, but benefited the Turks in the long term.