The Battle of Kosmidion (Turkish: Eyüp Muharebesi) occurred on 15 June 1410, during the Ottoman Interregnum, and was fought between the forces of the rival brothers, Musa Çelebi and Süleyman Çelebi, at Kosmidion (modern Eyüp) just outside the land walls of Constantinople.
The Byzantine emperor Manuel II Palaiologos was allied with Süleyman, whose army was encamped inside Constantinople.
[1] Manuel also prepared ships to help evacuate Süleyman's army in case of a defeat, but Musa managed to set them on fire before the battle began.
Laonikos Chalkokondyles claims that Vuk's brother Stefan also defected due to the pressure of Süleyman's ally, the Byzantine emperor Manuel II Palaiologos, but the chronicler Constantine of Kostenets reports that he fought alongside Musa in the battle, only to seek refuge with Palaiologos after the battle was lost.
[4] After the battle, Musa retreated to the area around Yambol and Chernomen in Bulgaria, while Süleyman recaptured the Ottoman capital of Edirne.