Thanks ct. The Roman conquest of Spain took a long time, and wasn’t finished until after the conquest of Gaul, oddly enough. Parts were in various hands, often under only nominal control of the Roman Senate, and chunks remained under Carthaginian rule, or local Punic rule, or was a patchwork of independent polities. Different factions ran around in Spain during the Pompeian war.
Yet there were portions under Roman rule, and/or fully colonized by Romans, in the 3rd c BC, through the 5th c AD, give or take Justinian’s reconquest.
The age of these coins are post-Diocletian; burial of it could mean anything from a barbarian invasion (or rumor thereof) to a rampaging legion trying to put their commander on the throne, to a legitimate emperor arriving to put down such a rebellion. The original owner probably died, or had to flee and could not return. Recovering that much weight and spiriting it across the countryside to a waiting vessel would be non-trivial, even if the person brought along the wain and oxen.
Tom Holland cites evidence in Rubicon that the Iberian Peninsula mining/smelting was so extensive after the Romans took over the Carthagenian mines that ash evidence is found in glacial layers in Iceland.