Quietus was an eastern Roman usurper during the tumultuous period following the capture of Emperor Valerian by the Persians in 260 AD. He was the son of Macrianus, a high-ranking military officer who had been left in charge of the eastern armies after Valerian's catastrophic defeat at Edessa. When Macrianus orchestrated the proclamation of his two sons, Macrianus Minor and Quietus, as co-emperors in 260, the brothers divided responsibilities: Macrianus Minor accompanied their father westward with a substantial army to challenge the legitimate emperor Gallienus, while Quietus remained in the East, probably in Syria, to maintain control of the eastern provinces and continue the war against Persia. Despite issuing coinage that proclaimed their legitimacy and adopting full imperial titles, the brothers' regime was built on unstable foundations, as they lacked the broader support necessary to sustain their claim against an established emperor.

The usurpation collapsed rapidly and violently in 261 AD. When father and son marched west to confront Gallienus, they were quickly defeated and killed in Thrace or Illyricum by Gallienus's general Aureolus. Left isolated in the East without his father's military support, Quietus found himself besieged in Emesa by Odaenathus, the powerful ruler of Palmyra who had remained loyal to Gallienus. Odaenathus captured the city and executed Quietus, effectively ending the Macriani usurpation after little more than a year.