Diocletian's scepter was once in the property of Emperor Diocletian of Rome. It held the power to raise the dead. The wielder of the scepter could resurrect a legion of Romans. It could only be wielded by a child of the Underworld and the legionaires would only follow an officer of Rome.
Impressed by Diocletian's career, Jason Grace and Reyna Ramírez-Arellano often fantasized about visiting Diocletian's Palace in Split, to retrieve the scepter. Because of Camp Jupiter's strict laws, Jason and Reyna knew they could never go there, but they made a pact that if one of them ever did, they would meet at Diocletian's Palace.
The scepter was a three-foot-long ivory staff topped with a dark globe of polished marble the size of a baseball and nestled on the backs of three gold Roman eagles. There is a black orb on top that glows purple.
In the The House of Hades , Nico obtained the scepter showing that it could only be wielded by a child of the Underworld and the legionaires would only follow an officer of Rome. The scepter allows Nico to summon zombie legionnaires to his aid - he can not control them however, as his is neither a Roman demigod nor a Roman officer. He used the scepter to summon zombies at the Necromanteion and Pompeii to fend off Gaea's forces, after which it exploded.
Believing it to be their best chance against Gaea's forces, Jason planned to head for Diocletian's Palace, leave Reyna a message, and retrieve Diocletian's scepter. He visited Diocletian's Palace with Nico di Angelo. After leaving a note for Reyna near Diocletian's tomb, the god Zephyros arrives and told them that the scepter had been taken by his master Eros long ago. Zephyros led Jason and Nico to his master to retrieve the scepter, warning them on how to deal with the god of love. As consequence for passing on the scepter, Cupid (Eros's Roman form) coerced Nico into revealing his romantic feelings for Percy Jackson, something that made Jason come to the conclusion that Cupid's wife, Psyche, had a point; Cupid was a monster. Later, on the group's way to House of Hades, it suddenly gets freezing cold. Nico thought it was from the scepter but it actually came from Khione, goddess of snow.
Upon their arrival in Epirus, the Seven brought with them Diocletian's scepter. Nico wielded it and reawakened the spirits of many dead Romans. He urged the spirits to attack the monster who escaped from the Doors of Death, but they wouldn't follow a Greek demigod. Jason, as praetor of New Rome, tried to lead the spirits. But, given his recent defection to Camp Half-Blood, Jason received no loyalty from the spirits any more than Nico did. At the last minute, Jason stepped down as praetor and promoted centurion Frank Zhang to praetor. In the end, the son of Mars led the spirits to victory against the forces of Gaea.
Nico used it to summon legionnaires to help Reyna fight the souls of Pompeii. The Scepter was fighting him and eventually exploded in Nico's hands. Hades later told him not to worry about it and that the scepter was so old it was surprising he even got two uses out of it.