Rare Roman-era silver ingots depicting Constantine the Great seized from alleged black-market sale

Three "truly sensational" Roman-era silver ingots depicting Constantine the Great were nearly sold illegally on the internet, a new investigation finds.

An unnamed man alleged that his great-grandmother found the rare artifacts buried in the family's backyard in Transcarpathia (also known as Zakarpattia), a region in western Ukraine. Later, the man reportedly tried to sell one of the silver bars online, according to Public Uzhgorod , Ukraine's public broadcast station.

However, officials from the museum intervened by reporting the attempted illegal sale to local law enforcement. When officers searched the home, they discovered two additional ingots. Because the ingots have "special cultural value," Ukraine's Office of the Prosecutor General has taken over the case, according to a translated statement from the National Museum of the History of Ukraine in Kyiv.

Each of the metal blocks, which are almost entirely pure silver, weighs more than 12 ounces (342 grams) and contains a coin-shaped impression of Emperor Constantine the Great on each side, according to the statement. Constantine, who ruled from A.D. 306 to 337, is known for ushering Christianity into the Roman Empire and moving his capital to "New Rome," which later became Constantinople (modern-day Istanbul) .

The ingots would have been used during the minting process to strike coins known as siliquae. The coins with Constantine's likeness would have been issued between A.D. 310 and 313 in Augusta Treverorum, a Roman city that today is Trier, Germany. At one time, the pieces would have been batched together with a thin, silver ribbon, which has since been lost, according to the statement.

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"Three ingots fastened together were supposed to be a gift for a very high-ranking person," Maksym Levada, a curator at the museum, said in the statement. "The fact that they were found outside the Roman Empire on the territory of modern Ukraine makes them an invaluable source of our past."

Experts estimate the treasure's value at 3.5 million Ukrainian hryvnia, or about $84,800.

"But what makes them unique is not the cost, but the fact that only a few similar ingots have been found in Europe to date," Andriy Kostin , Ukraine's prosecutor general, said in the statement.

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There are about 90 known Roman silver ingots in existence today, with only 11 containing mint stamp impressions, making the three ingots' recovery even rarer, according to the statement.

Kyrylo Myzgin , an archaeologist and faculty member at the University of Warsaw who initially examined the ingots, told Live Science in an email that the finding "can be considered truly sensational."

"It is excellent news that they ended up in a museum rather than on the black market for antiquities," Myzgin said. "Roman silver ingots with coin die imprints are incredibly rare and were virtually unknown outside the Roman Empire. It is likely that these ingots reached the territory of what is now western Ukraine as a result of interactions between the local population — possibly Germanic tribes or Dacians [people in what is now largely modern-day Romania] — and the Roman Empire in the early 4th century. However, the exact nature of these interactions has yet to be determined."

The ingots are now on display in the museum's "Salvated Treasures" exhibition, which contains a collection of rescued artifacts.