Olympian Providence: A Grimdark Science Fantasy Retelling (The Olympian Series Book 1) by D.B. Harris

"They were created to end a war in the stars. Instead, they became the gods of our past." Earth is a dying husk, and the Colonies are starving. In the resource-starved trenches of a solar system at war, Allen Quinn was never meant to be a hero. He was meant to be a weapon. As a "Titan" of the Europan militia’s Cadmus Project, Allen’s body is a temple of illegal nanotechnology—until a catastrophic execution hurls him 3,000 years back into the white-marbled cradle of Ancient Greece.