Syrmus or Syrmos (also Syrmios, Ancient Greek: Σύρμος) was a king of the West Thracian Triballi tribe during the 330s BC.
[2] After the death of his father, Philip II, Alexander the Great passed through the lands of the Odrysians in 335-334 BC, crossing the Haemus ranges and after three encounters (including the Battle of Haemus) defeated and drove the Triballians to the junction of the Lyginus at the Danube.
Syrmos and his people took refuge on the Danubian island of Peukê where the remnants of defeated Thracians were gathered.
Alexander was satisfied with his victories and accepted peace so he could focus on the battles ahead in Asia.
[3] Though Syrmus was later considered the eponymous founder of Sirmium,[4] the roots are different, and the two words only became conflated later.