Æ20 - Valerian and Gallienus COL AVG TROAD

Alexandria Troas was a Roman colony — hence the COL(onia) AVG(usta) designation — founded by Antigonus and refounded under Augustus, who resettled it with veterans and granted it Italian legal status. The city maintained an unusually active bronze coinage into the third century, long after many Asian mints had gone quiet. The joint reign of Valerian and Gallienus, 253–260, ended abruptly when Valerian was captured by Shapur I at the Battle of Edessa — the only Roman emperor taken prisoner by a foreign enemy — after which Gallienus ruled alone and the paired titulature disappeared from colonial issues.