Emidius was a Catholic bishop ordained by Pope St. Marcellus. He lived during the reign of the Roman Emperor Diocletian, who ruled 284AD-305AD. Diocletian was not fond of Christians. Emidus was sent to preach the gospel in Trier, but he ran into trouble when he began smashing the locals' non-Christian religious icons. He had to flee to Rome, to no avail; he was beheaded on August 5, 303.
Part of his skeleton resides as a relic in the cathedral at Ascoli Piceno, Italy; he has long been considered the patron saint of that city. He is also the patron saint of protection against earthquakes.
Emidius' feast day is Aug. 9th. In 1869, Pope Pius IX (at the request of Archbishop Joseph Alemany) set that day as a day for prayers against earthquakes.
Emidus has been further immortalized in a variety of artwork. The best-known piece is an oil painting entitled "The Annunciation with St. Emidius" which was completed by Renaissance artist Carlo Crivilli in 1486.
The Roman Ritual translated by Philip T. Weller, S.T.D. 1964.