Joannes

Ioannes, (Latin: Iohannes Augustus) known in English as Joannes or even John, was a Roman usurper (423–425) against Valentinian III.

On the death of the Emperor Honorius (August 15, 423), Theodosius II, the remaining ruler of the House of Theodosius hesitated in announcing his uncle's death. In the interregnum, Honorius's patrician at the time of his death, Castinus, elevated Joannes as emperor.