Saint Mardonius and those with him suffered with St Anthimus during the persecution against Christians under the emperors Diocletian (284-305) and Maximian (305-311). The persecution became particularly intense after a fire at the imperial court at Nicomedia. The pagans accused the Christians of setting the fire and reacted against them with terrible ferocity.
In Nicomedia alone, on the day of the Nativity of Christ, as many as twenty thousand Christians were burned inside a church. However, this monstrous inhumanity did not frighten the Christians, who firmly confessed their faith and endured martyrdom for Christ.
Sts Dorotheus, Mardonius, Migdonius, Peter, Indes and Gorgonius died during this period. One of them was beheaded by the sword, others perished by burning, or being buried alive, or by drowning in the sea.