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Gaius Acilius (fl. 155 BC) was a senator and historian of ancient Rome. He knew Greek, and in 155 interpreted for Carneades, Diogenes, and Critolaus, who had come to the Roman Senate on an embassy from Athens.
Acilius wrote a history of Rome in Greek that went from the earliest times to at least 184 BC (according to Dionysius of Halicarnassus), and it appeared around 142 BC (mentioned in Livy). The work was translated into Latin by a Claudius, most likely Claudius Quadrigarius, but only fragments survive.