When the popular Nestorianism of the Syrians was condemned at Ephesus (431) it began to gravitate eastwards, Nisibis becoming its eventual headquarters; but Edessa and the western Syrians refused to bow to the Council of Chalcedon (45r) when it condemned Monophysitism.
As Eutychianism is the doctrine that the God-man has only one nature, so Nestorianism is the doctrine that He has two complete persons.
Another early Monophysite was Simeon of Beth Arsham, who by a series of journeys and disputations within the Persian empire did all he could to prevent the triumph of Nestorianism among the Persian Christians.
Western Syria, on the contrary, had partaken with Alexandria in the reaction from Nestorianism which finally crystallized in the Monophysite doctrine, that spread so widely through Egypt and Western Asia towards the end of the 5th century.
By violence, in attaching to Nestorianism nearly all the Christian communities of Persia, with the exception of Taghrith, which was always strongly Monophysite.
Thus the council rejected both Nestorianism and Eutychianism, and stood upon the doctrine that Christ had two natures, each perfect in itself and each distinct from the other, yet perfectly united in one person, who was at once both God and man.
Those who have gone over from Nestorianism to Catholicism, seems to be the most important; there are also Syrian Catholics and Jacobites.
The union even then met with resistance from a number of bishops, who, rather than accede.to it, submitted to deposition and expulsion from their sees; and it was not until these had all died out that, as the result of stringent imperial edicts, Nestorianism may be said to have become extinct throughout the Roman empire.