Macrinus- Marcus Opelius Macrinus was born of very humble parents in AD 164. After holding various appointments in the imperial household, he became prefect of the Praetorian guards under Caracalla. He commissioned the murder of the unpopular emperor on April 8, 217 AD and several days was hailed emperor. He suffered a minor defeat to the Parthians, but the terms were so unfavorable to the Romans that Macrinus lost much of his popularity. A conspiracy, fostered by Julia Maesa, sister of Julia Domna, in favor of her grandson Elagabalus caused the Syrian army to revolt. In the struggle Macrinus was defeated and fled to Chalcedon, but was captured and put to death along with his son Diadumenian after a reign of only 14 months.
Fides- good faith, loyalty, trustworthiness. In conjunction with militum, good faith of the soldiers.