Born in Thessaloniki. His childless parents prayed to God for him. When his father, the Duke of Thessaloniki, died, Emperor Maximian appointed Demetrius as Duke in his father's place and specifically recommended that he persecute Christians. But instead of persecuting Christians, Demetrius publicly confessed Christ in Thessaloniki. When the emperor came to Thessaloniki, he summoned Demetrius and when he confessed his faith in Christ before him, he threw him into prison. Knowing what awaited him, he left all his property to his disciple Lupus to distribute to the poor. An angel of God appeared to him in prison and strengthened him. After a few days, by order of the emperor, soldiers pierced him with spears in prison. As the protector of Thessaloniki, he saved this city many times. In Russia, he is considered the protector of Siberia.

Venerable Martyr Joasaph. Commemoration of the Great Earthquake in Constantinople.