Workers near Zaudin Park in Tomares, a suburb of the city of Seville in Spain, were digging water lines when they noticed an anomaly about three feet underground. When they looked closer, they found 19 amphora—a type of earthenware container that ancient cultures used to transport everything from wine and olive oil to fish, fruits, nuts and grain. But the contents of these amphora weren’t perishable: they contained 1,300 pounds of Roman coins from the third and fourth centuries A.D.

The find is remarkable, not only for its the sheer size, Fred Barbash at the Washington Post reports, but also because the money appears to have never been circulated, making them some of the best-preserved coins ever discovered.

At a press conference, Ana Navarro, head of Seville’s Museum of Archaeology revealed that most of the coins were minted with images of emperor Constantine, who ruled the Roman Empire from 306 to 337 A.D., and Maximian, who held the post from 286 to 305 A.D. “It is a unique collection and there are very few similar cases. The majority were newly minted and some of them probably were bathed in silver, not just bronze,” Navarro said. “I could not give you an economic value, because the value they really have is historical and you can’t calculate that.”

The Local reports that amphora used to hold the coins were smaller, specialized containers used specifically for treasure. According to Barbash, the researchers think the vast coin hoard was a shipment meant to pay taxes or to pay the Roman army in Spain. It is not known why it was never distributed or why it ended up under a park in Tomares.

Though they have not yet tallied up the number of coins found, it is likely spectacular. It was big news in 2015 when a 33-pound stash of more than 4,000 Roman coins from the time of Emperors Maximian and Aurelian was unearthed in Switzerland. Another significant hoard of more than 3,000 coins was found in southeast Britain earlier this year. The stash of coins in Seville dwarfs those finds many times over.