After the early School of Antioch came into decline, the presbyter Diodore of Tarsus re-founded it in the middle of the fourth century as a semi-monastic community. He was a native of Antioch who had studied philosophy in Athens together with his friend Basil of Caesarea. In Antioch he became famous for his orthodox steadfastness against the Arian bishops that ruled the city at that time. In 378 Diodore left Antioche to become Bishop of Tarsus and his student Theodore of Mopsuestia became the new head of the school.
Diodore and Theodore were strong opponents of the heresy of Apollinaris, who maintained that Christ was the divine word dwelling in a human body, but without a human soul. In response, they insisted that Christ had both a divine and a human soul, which were connected but distinct. The Alexandrian school on the other hand taught a union of the two persons of Christ.
The teaching Diodore and Theodore is the foundation of the Assyrian (Nestorian) theology.
Diodorus was at the Councils of Antioch in 379 and of Constantinople in 381.
Diodorus rejected the allegorical interpretation of the Alexandrians, and adhered to the literal sense.
It seems certain that Diodorus went too far in his opposition to (the younger) Apollinarius of Laodicea, according to whom the rational soul in Christ was supplied by the Logos.
Tarsus was already the caput Ciliciae, the metropolis, where the governor resided.
The greatest glory of Tarsus is that it was the birthplace of St. Paul (Acts 9:11; 21:39; 22:3), who took refuge there after his conversion (Acts 9:30), and was joined by Barnabas (Acts 11:25).
Tarsus, which has preserved it name, is a caza of the vilayet of Adana on the railroad from Adana to Mersina; the city numbers about 18,000 inhabitants, of whom 10,000 are Mussulmans, the remainder are Greek or schismatic Armenian.