Mamurius was tasked by King Numa with crafting eleven identical ancile to the one the gods gave him to protect Rome.
After his death he became a ghost and haunted the forges of Camp Jupiter.
In late January or early February following the Second Demigod Civil War, he was lured to the Temple of Mars by Elon, a young faun, and trapped in a bottle. Elon demanded he reveal the real ancile to him but he refused, causing Elon to take the shields down one at a time until he found the right one.
He and Blaise team up with Claudia and Janice to find the missing ancile. After learning Claudia is confined to her bunk, he and the others come clean to Frank Zhang and tell the praetors their plan, they approve. After leaving the Via Praetoria, he tracks Elon down and forces the young faun to guide Claudia, Janice and Blaise through the hidden tunnels to the dump.
After the ancile is retrieved he is given a spot on the wall of fallen heroes in the library of New Rome University.