Julius is a Roman demigod son of Mars with three years of service to the legion.
History
Julius was born to Mars, the Roman god of war, and an unnamed human mother. When he was old enough, the son of Mars was sent to the Wolf House to be trained judged by Lupa. After surviving his training, he made his way south to Camp Jupiter and was accepted into the legion as a probatio before becoming a full member of the twelfth.
The Trials of Apollo
Camp Jupiter Classified: A Probatio's Journal

When he has sentry duty with Claudia, the son of Mars scuffs when the legacy of Mercury says she has to use the bathroom. When Claudia returns, she tells him about hearing a mysterious voice in the bathroom before going in and he says it was probably a naiad and a faun meeting up in secret.