Dinero 'negro' - Alfonso X

Alfonso X initiated a sweeping monetary reform in 1258 that replaced the old pepiones with a new billon coinage deliberately debased to a lower silver content — hence the popular designation "negro," referring to the coin's dark, copper-heavy appearance after oxidation. The reform was partly a fiscal measure to fund Alfonso's expensive and ultimately failed campaign to be elected Holy Roman Emperor, a pursuit that drained Castilian resources through the 1260s.

The alloy was set at roughly one part silver to several parts copper, placing it among the most debased issues of Alfonso's otherwise ambitious monetary program.