4 Reales - Philip III

The Potosí mint was established in 1572 to process the extraordinary silver output of Cerro Rico, the mountain that effectively bankrolled the Spanish crown's European wars and colonial administration for over two centuries. By the time Philip III ascended in 1598, the mint was producing cobs — macuquinas — on an industrial scale, with quality control that was, charitably, inconsistent. This 4 reales denomination sat at the practical midpoint of everyday colonial commerce, too large for small transactions, too small for major merchant settlements.

The Potosí assayers of this period were later implicated in systematic fraud — systematically short-weighting cobs and pocketing the difference in silver. The scandal, which broke fully in 1649, cast retroactive suspicion on decades of output.