Tostão 'P-O' – João III 3rd type, Porto

The tostão denomination — equivalent to 100 réis — was João III's workhorse silver coin for Iberian and overseas trade during an era when Portugal's empire stretched from Brazil to Malacca. The Porto mint's output during this specific window, 1555–1557, falls in the final years of João III's reign; he died in June 1557, leaving a three-year-old grandson as his heir and triggering a regency crisis. Porto production was always subsidiary to Lisbon, and surviving examples attributable to this mint carry a meaningful premium in completeness of the mintmark punch.

Gomes distinguishes J3 140 and J3 141 by die variations in the cross arrangement — a granular distinction that matters considerably for specialist attribution.