Potosi eight reales

The Potosí eight reales, also known as a Spanish dollar or piece of eight, is a large silver coin struck at the Potosí mint in modern-day Bolivia under the Spanish Empire. The eight-real denomination was originally instituted during a Spanish monetary reform in 1497. Following the exploitation of vast silver deposits discovered at Potosí, the local mint became one of the primary New World facilities producing these silver pieces, which circulated globally across the Americas, Europe, and Asia as an international trade currency.

From 1572 until 1773, silver colonial coins from the mint were struck as cobs. These early specimens were cut from silver bars and struck by hammer on coin dies, rendering them irregular in shape and strike, though accurately weighed. Mint workers occasionally clipped over-thick blanks to achieve the required standard. Following the introduction of screw presses after 1732, more uniform cobs were manufactured alongside round, machine-milled coinage known as columnarios, which were produced between 1732 and 1773 to deter illegal clipping.

Silver eight-real pieces produced in the Americas are distinguished from those struck in mainland Spain by the inclusion of the Pillars of Hercules. On machine-milled columnario issues, the reverse portrays two crowned globes representing the Old and New Worlds above sea waves, flanked by ribbon-wrapped pillars inscribed "PLUS ULTRA", beneath the motto "VTRAQUE VNUM" alongside the date and mint marks. The obverse displays a crowned Spanish shield flanked by the assayer mark and denomination, accompanied by a protective edge bearing a repeating laurel leaf pattern. Earlier cob pieces are typically recognised by their crude, irregular outline and the PTS monogram.