Æ21 - Valerian and Gallienus ΚΟΙΝΟΝ ΘΕϹϹΑΛΩΝ, Δ

The Koinon of Thessaly — a federal league of Thessalian cities — retained the right to strike provincial bronze under Roman oversight well into the third century, issuing coins in the joint names of co-emperors as a deliberate display of loyalty to whichever pair held power. The Δ on this piece is a series or magistrate mark used to organize production runs, a common administrative device in Thessalian coinage of this period that scholars have not yet fully mapped to specific officinae or mint sequences.

Valerian's capture by Shapur I at Edessa in 260 ended the joint reign and effectively terminated this series.