The bust, believed to be of Julius Caesar, is a realistic portrait of a man in his 50s. (France Ministry of Culture)

A bust found at the bottom of a river in Arles, France, may be the truest representation of Julius Caesar ever found.

The marble sculpture of a man in his 50s, with facial wrinkles and a receding hairline, may have been carved from life.

Archeologists say the bust dates from 49 to 46 B.C. when Caesar reigned and the town of Arles was founded.

It also resembles official portraits of Julius Caesar from coins struck in his lifetime.

"I suspect the bust was thrown in the river after he was assassinated because it would not have been good at that time to be considered a follower of his," said French archaeologist Luc Long, quoted by Agence France Presse.

"In Rome you don't find any statues of Caesar dating from the time he lived. They were all posthumous," he added.

Three other statues, including one of the god Neptune, were found at the bottom of the River Rhone.

Caesar used Arles as a base for his campaign against Pompey, his rival for leadership of the Roman Empire. Caesar defeated Pompey and Pompey was later assassinated.

The bust was likely carved to honour Caesar as a patron of the city. It is in the realistic style fashionable in his time, unlike posthumous portraits which were made more attractive.

Culture Minister Christine Albanel congratulated the archaeologists on finding a unique object that enriched the world's heritage.