Dinero 'prieto' - Alfonso X Seville

Alfonso X's billon dineros prietos — "dark pennies," named for the blackened appearance of their debased silver-copper alloy — were issued as part of a prolonged monetary crisis that plagued his reign. Facing chronic fiscal shortages from his campaigns and his expensive, ultimately failed bid for the Holy Roman Imperial crown, Alfonso repeatedly debased the coinage, provoking formal complaints from the Castilian Cortes at Burgos in 1269. The prieto issues were the direct result of that debasement policy, authorized despite noble and merchant resistance.

Seville's mint was among the most active under Alfonso, having only recently come under Castilian control following Ferdinand III's conquest of the city in 1248.