By the 500s, Marinus had emerged as "the most trusted adviser" (John B. Bury) of Anastasius, and was rewarded with his nomination to the praetorian prefecture of the East, probably in early 512. He seems to have held the post until early 515.; . In autumn 512, Marinus encouraged Anastasius to openly support the Monophysite version of the Trisagion, which the Patriarch Timothy had inserted into liturgy even in the Hagia Sophia. As a result, the mostly Chalcedonian population of Constantinople launched a major riot on 4 November against the "heretical" version, forcing Marinus and Plato, the urban prefect, to respond with force in an attempt to quell the disturbance. The clashes continued, however, and on 6 November the Chalcedonian populace gathered in the Forum of Constantine and launched a riot that nearly cost Anastasius his throne: Anastasius's statues were thrown down, the aged general Areobindus, related by marriage to the Theodosian dynasty, was proclaimed emperor, and Marinus's house was torched. It took a personal appearance by Anastasius in the Hippodrome of Constantinople to calm the crowds, who demanded that Marinus and Plato be thrown to the beasts.; .
