In the first part of the sixth century, variant forms of Monophysitism existed. In 'Christology after Chalcedon', Iain Torrance provides a theological introduction and a translation of the letters between Severus of Antioch and Sergius the Grammarian. Severus was the Monophysite Patriarch of Antioch - a leader of the moderate Monophysites whose doctrine adhered more closely to Catholic teaching and whose primary divergence from orthodoxy was terminological. Though little is known of Sergius, it is apparent from his letters that he was a Monophysite of the more extreme sort. The correspondence between Sergius and Severus comprises three letters from Sergius, three replies by Severus, and an apology by Sergius.