Between 171 and 168, Philip's heir Perseus engaged the Roman Republic in the Third Macedonian War. Perseus' most trusted ally in this war was the Thracian king Cotys, whom the historian Polybius calls an Odrysian. He fought in the battles of Callinicus and Pydna, but eventually became a Roman ally after the war. Perhaps he is identical with the Cotys mentioned by the historian Strabo. However, his Odrysian background has been doubted, as the account of Polybius, the only remaining source (minus Livy, who relied on Polybius), called him an Odrysian only once, while also calling the Getic king Dromichaetes an Odrysian. It may thus be likely that Polybius used "Odrysian" as a synonym for "Thracian". Furthermore, after the war Cotys was described as being active in the hinterland of Abdera at the Aegean coast, implying that he was rather a Sapaean king, who are known to have resided in the Rhodopes. His identity must remain uncertain. It is a fact, however, that Cotys was the last king in the sources to be explicitly labelled an "Odrysian". There is also no evidence that Odrysians had any affiliations with the royal houses of the Sapaeans and Asti of the 1st century BC.