Peter III of Raqqa (Latin: Petrus Callinicus; Peter of Callinicum), was the Patriarch of Antioch and head of the Syriac Orthodox Church from 581 until his death in 591.
Peter was born in the 6th century in the city of Raqqa, here he became fluent in Greek and Syriac as well as obtaining a fair knowledge of philosophy and theology. Peter replaced his father, Paul II, upon his death in 581 and was consecrated patriarch by Pope Damian of Alexandria at the Mor Hananyo Monastery.
Afterwards, Peter traveled to Alexandria to promote religious ties with the Patriarchate of Alexandria. Whilst here, however, Peter was accused of Tritheism by Pope Damian of Alexandria and in turn accused him of Sabellianism. Peter replied to the accusations at length in his Adversus Tritheistas or Many-lined Letter.
The work abounds in citations from earlier Greek authors, including the Cappadocians, John Chrysostom, Cyril of Alexandria as well as Severus of Antioch, translated into Syriac. It deals intensively with the theological and philosophical terminology involved with and illustrates the consequences of the rejection of the Chalcedonian Definition in Syriac monastic circles. This created a schism between the Alexandrian and Antiochene churches that lasted for almost a decade after Damian's death.