Original: It traces its origins to the See of Seleucia-Ctesiphon in central Mesopotamia, which tradition holds was founded by Saint Thomas the Apostle (Tooma Shlikha) as well as Saint Mari and Saint Addai in 33 A.D. as asserted in the Doctrine of Addai.
Simplified: It traces its origins to the See of Seleucia-Ctesiphon, started by Saint Thomas the Apostle as well as Saint Mari and Addai as shown in the Doctrine of Addai.