Rare Coin Minted by Marcus Junius Brutus After He Helped Assassinate Julius Caesar Will Go to Auction

The gold coin — one of only 17 of its kind known to exist — dates to 43 or 42 B.C. and depicts Brutus on the front and a trophy celebrating a naval victory on the back.

A rare gold coin minted by Marcus Junius Brutus after he helped assassinate Julius Caesar will go to auction next week. The coin, which dates to 43 or 42 B.C., is one of only 17 of its kind known to exist. It will be sold by Numismatica Genevensis SA on Dec. 9-10.

The coin depicts Brutus on the front and a trophy celebrating a naval victory on the back. It is an aureus, which was worth 25 denarii, or roughly a month's pay for a Roman soldier at the time.

On the Ides of March in 44 B.C., Brutus and co-conspirator Gaius Cassius Longinus led dozens of men to a meeting of the Roman Senate. Their plan was to murder Caesar, as they thought his growing power threatened the Roman Republic. Caesar was stabbed 23 times, and as he lay dying, he famously chastised his close friend Brutus for his role in the plot. (Although Caesar spoke to Brutus in Greek, this interaction was later dramatized by William Shakespeare with the Latin phrase "Et tu, Brute?" which translates to "Even you, Brutus?")

Although many senators and other Roman leaders participated in Caesar's assassination, the Roman people were outraged by the news. Within months, Brutus and Cassius went into exile, attempting to take over the eastern provinces, while Caesar's allies stayed in Rome.

To pay his soldiers, Brutus minted coins such as the silver denarius, which was worth about a day's pay, and the gold aureus, which was equivalent to 25 denarii, or roughly a month's pay.

The disagreements between the conspirators and allies eventually forced a civil war that lasted from 43 to 42 B.C., ending when Caesar's allies defeated Brutus and Cassius at the Battle of Philippi in Greece.

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The rare gold coin going up for auction is an aureus that was struck before the Battle of Philippi and has a portrait of Brutus on the front.

"The title BRVTVS IMP(erator) on the obverse refers to the military victory over the Thracian tribe of the Bessi, who opposed Brutus's control of the area in 43 BCE," Lucia Carbone, an associate curator of Roman coins at the American Numismatic Society, told Live Science in an email.

The back of the coin includes two conjoined ships' prows (the forward-most part of the bow), which represent Brutus' and Cassius' naval victories in 42 B.C., Carbone said. Somewhat ironically, "the victories celebrated on this aureus were the direct cause of their final defeat in Philippi," she said, because they were stretched thin by fighting on two fronts. In addition, the back references Publius Servilius Casca Longus, one of the co-conspirators and possibly the first person to stab Caesar.

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One reason this coin is so rare is that only six stamp dies — two for the front and four for the back — were used to create the design, which was issued for a very short time. The coin also comes from a large and important collection of Roman coins owned by the early 20th-century Italian politician Giuseppe Mazzini, Carbone said.

"While coin collectors have long prized coins previously owned by famous collectors or scholars, these object histories are even more critical today, in light of growing legal and ethical concerns around collecting," Liv Yarrow, a Roman historian at the City University of New York, told Live Science in an email.

This aureus was last sold in 2006