Solidus - Grimoald III and king Charlemagne

Grimoald III ruled Benevento as a Lombard prince under Frankish overlordship following Charlemagne's conquest of the Lombard kingdom in 774, and this joint coinage reflects the uneasy political arrangement imposed on him. Charlemagne demanded his name appear on Beneventan issues as a visible assertion of Frankish suzerainty — Grimoald complied, but only just, and would later drop the Carolingian name entirely after 792 when he felt strong enough to assert independence.

That post-792 break makes this issue precisely datable by the presence of Charlemagne's name alone.