Gaius Caesar Augustus Germanicus (nickname: Caligula, 12 AD - 41 AD), posthumously known as Caligula, was 37 AD -41 AD Roman Emperor. Woodcut engraving, published in 1864. (iStock)  (ZU_09) 

The "party boats" of Roman Emperor Caligula were so legendary that Benito Mussolini partially drained a lake in order to find two of them a century ago.

But there was one Mussolini may have missed. Researchers believe a third wooden vessel on which Caligula is said to have hosted orgies during his brief reign 2,000 years ago is still hiding in the depths of Lake Nemi, about 20 miles from Rome, where it came to rest for unknown reasons.

"We know from documents from the 15th century that one of the boats went down in an area of the lake different to where the other two were found during the Fascist era," Nemi mayor Alberto Bertucci tells theTimes of London.

With help from police and Civil Protection Agency divers, researchers now hope to find it. On Wednesday, those divers will begin user sonar to scan the muddy lake for the missing ship, which may have been built to honor the goddess Diana, reports the Telegraph.

The ships were said to have been decorated in gold and marble, with purple silk sails, columns, bronze statues, and even plumbing and heating. If found, however, this will be the only "party boat" of Caligula's still in existence.

The remains of the two vessels—"among the largest in the ancient world" at up to 240 feet long, per International Business Times— found in Lake Nemi between 1928 and 1932 were kept in a museum that was destroyed in a fire during World War II.

Only a few bronze statues survived, though small-scale replicas were later built in the boats' place. (What hasn't been found: The tomb of Caligula, who was stabbed to death less than 4 years into his reign.)

This article originally appeared on Newser: Search Is On for Caligula's 2K-Year-Old Orgy Boat