Æ21 - Valerian and Gallienus ΝΙΚΑΙΕΩΝ

Nicaea was one of the most prolific provincial mints in Bithynia, striking bronze for a succession of emperors well into the third century. The joint reign issues of Valerian I and Gallienus reflect a deliberate co-emperorship that Valerian instituted immediately upon his accession in 253 — elevating his son to secure dynastic continuity in the face of simultaneous threats on the Rhine and Euphrates frontiers. That arrangement ended abruptly in 260 when Valerian was captured by Shapur I at the Battle of Edessa, the only Roman emperor ever taken prisoner by a foreign enemy.