Antoninus (Marcus Aurelius Antoninus), was Roman emperor from 198 to 217. He was a member of the Severan dynasty, the elder son of Septimius Severus and Julia Domna. Co-ruler with his father from 198, he continued to rule with his brother Geta, emperor from 209, after their father's death in 211. His brother was murdered by the Praetorian Guard later that year, supposedly under orders from Caracalla himself, who then reigned afterwards as sole ruler of the Roman Empire. He found administration to be mundane, leaving those responsibilities to his mother, Julia Domna, to attend to. Caracalla's reign featured domestic instability and external invasions by the Germanic peoples. Caracalla's reign became notable for the Antonine Constitution (Latin: Constitutio Antoniniana), also known as the Edict of Caracalla, which granted Roman citizenship to all free men throughout the Roman Empire. The edict gave all the enfranchised men Caracalla's adopted praenomen and nomen: "Marcus Aurelius".