Æ23 - Valerian and Gallienus ΚΟΙΝΟΝ ΘΕϹϹΑΛΩΝ, Δ

The Thessalian Koinon was a federal league whose coinage rights under Roman rule were carefully negotiated rather than assumed — provincial bronze issues like this one required imperial sanction, and the joint naming of Valerian and Gallienus as co-emperors dates the issue precisely to the period after Gallienus was elevated to Augustus in 253. The Δ countermark denotes a denomination within the Koinon's internal tariff system, a feature specific to Thessalian federal issues and not replicated in neighboring provincial mints.