A 2,000-year-old sapphire ring belonging to the Roman Emperor Caligula, depicting his wife Caesonia

The nearly 2,000-year-old sapphire ring is a wonderful piece of jewelry, but its history makes it all the more fascinating.

It’s thought to have belonged to Caligula, the notoriously tyrannical ancient Roman emperor. Caligula ruled from 37 CE, but his reign was cut short after four years when he was assassinated by Praetorian Guards—the security force that was meant to protect the emperor.

Women on a ring appears to be a portrait of Caligula’s fourth—and last—wife, Caesonia. Roman historian Suetonius described her as “a woman of reckless extravagance and wantonness” and even claimed that she gave birth to their daughter on their wedding day.

Caligula and Caesonia had a passionate affair and its said that he even occasionally showed her off, naked, to friends. With such a fiery relationship, it’s no wonder that the emperor would want her portrait on his ring. Alas, their love wouldn’t last, with Caesonia—and her daughter—being murdered just hours after Caligula was killed.

The ring was in the famed intaglio gemstone collection assembled by George Spencer, 4th Duke of Marlborough, in the second half of the 18th century. Before that, it was part of a smaller but also renown group of engraved gems collected by Thomas Howard, Earl of Arundel, in the first half of the 17th century. Via marriage and descent, Lord Arundel’s gemstone collection was added to the extremely fine pieces the Duke of Marlborough had bought from dealers and private owners on the continent.