URI historian and underwater explorer Bridget Buxton is trained to search for knowedge, not sunken treasure—but her most recent expedition to Israel dug up plenty of both.

In February 2015, scuba divers in Israel’s eastern Mediterranean found 2,580 gold coins on the ocean floor inside the ancient Roman port of Caesarea. It was the biggest hoard of gold coins ever discovered in Israel, and made headlines last year. This year, Buxton and her colleague John Hale from the University of Louisville revealed how the underwater dig unfolded.

Hundreds of coins were hidden under rocks and sand, but couldn’t be moved until researchers made a detailed map of the area. “The excavation of a site destroys it,’’ Buxton explains, “so we need to record all possible clues.’’

Buxton and the other archaeologists created a map with the Pladypos robot, brought over by the team’s Croatian partners. After mapping the site and removing a layer of rocks from the sea floor, Buxton and her colleagues discovered a second pocket of coins, bringing the total hoard to about 3,000.

The most important discovery, however, was a 10-centimeter iron spike with coins cemented to either end, proof that the gold came from a wooden shipwreck that sank sometime around 1036 A.D. “We guess that the ship was coming in to Caesarea and struck one of the semi-submerged ruins of the old Roman breakwater,’’ Buxton said. “What we don’t understand is how such a large amount of gold was never recovered, since the ship sank so close to shore in very shallow water.’’

Robert Kool of the Israel Antiquities Authority identified the coins as dinars minted by the Islamic Shia dynasty called the Fatimids. The dynasty ruled most of North Africa and the Holy Land on the eve of the First Crusade, which captured Jerusalem from the Fatimids in 1099.

Caesarea Maritima was a strategic city for the Fatimids throughout the 11th century, and the gold might have been intended as pay for a local garrison, Buxton said. Many of the coins are from the reign of a controversial Caliph, al-Hakim, a revered figure in the Druze branch of Shia Islam, she said.

Buxton and her Croatian and Israeli colleagues plan to continue their underwater research this May.