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Researchers have used an unmanned underwater vehicle to carry out a non-intrusive investigation of an 18th-century AD shipwreck in the Colombian Caribbean, revealing it is likely the San José Galleon, the lost flagship of one of the most-important cargo fleets of the Hispanic Monarchy. The study is published in Antiquity.

Between the 16th and 18th centuries AD, the Hispanic fleets transported royal cargo from American territories to the Iberian Peninsula.

One such fleet was the Flota de Tierra Firme, which connected Cadiz with the New Kingdom of Granada and the Viceroyalty of Peru.

"The Tierra Firme Fleet, commanded by the San José Galleon, held the exclusive monopoly on transporting royal treasures between South America and the Iberian Peninsula," states lead researcher on this topic, Daniela Vargas Ariza from the Escuela Naval de Cadetes Almirante Padilla and Instituto Colombiano de Antropología e Historia—ICANH in Colombia.

Historical sources indicate that the galleon was sunk off the coast of Colombia during a battle with the British in AD 1708, while transporting a large and varied cargo. However, physical remains of the ship had never been found, and its location was unknown.

To determine whether the ship was indeed the San José, the Colombian navy used an unmanned, remotely operated underwater vehicle to survey the wreck non-invasively.

The Colombian government located the shipwreck in 2015, but the coins seen there had not been identified until recently, as they have not been recovered from the site.

A three-dimensional reconstruction was created using photogrammetry on high-resolution digital images of the coins, carefully captured by the underwater vehicle. This process allowed for a detailed examination of their surface features. By combining the reconstruction with information from multiple sources, researchers were able to establish the timeframe of the ship's sinking: after 1707, the year the coins were minted.

"Coins are crucial artifacts for dating and understanding material culture, particularly in shipwreck contexts," says Vargas Ariza. "Hand-struck, irregularly shaped coins—known as cobs in English and macuquinas in Spanish— served as the primary currency in the Americas for more than two centuries."

The researchers identified symbols on the coins' surfaces that indicate they were minted in AD 1707 in Lima, as well as heraldic symbols of the crowns of Castile and Leon.

This means that the ship was indeed a Hispanic galleon and it must have sunk after 1707. Historical records suggest these coins were part of a large treasure dispatch from Peru that year, in which the San José Galleon took part and was sunk.

Therefore, a decade after its discovery, this new research enhances the evidence associating the shipwreck with the San José Galleon, advancing—but not concluding—the ongoing state-led investigation. It also shows how powerful coins can be in archaeological investigations.

"This case study highlights the value of coins as key chronological markers in the identification of shipwrecks," concludes Vargas Ariza. "This find presents a rare opportunity to explore an underwater archaeological site and deepen our understanding of 18th-century maritime trade and routes."