Archaeologist Luc Long said the marble bust was sculpted when Caesar was still living and probably thrown into the river after the ruler's assassination in 44 B.C., ANSA reported Wednesday.
"It wouldn't have been a good idea to show you were his supporter right then,'' Long said.
The bust, which showed Caesar as wrinkled and bald, was probably sculpted two years before his death, the French culture ministry said.
Arles was Caesar's base for his campaign against Pompey, ANSA said.
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