Lucius was a soldier of the Roman army. He'd enlisted after impregnating a young woman, and decided that he did not want to face his father's wrath. He was part of General Pontius Pilate's expedition to put down a rebellion in Jerusalem. The leader of that rebellion was the Chieftain known as the Son of God.
After fierce fighting, the rebellion was defeated. Lucius and his comrade Marcus were able to identify the Son with the help of one "Red Beard" and deliver him to General Pilate.