The Doctrine of Addai (Syriac: ܡܠܦܢܘܬܐ ܕܐܕܝ ܫܠܝܚܐ Malp̄ānūṯā d-Addai Šlīḥā) is a Syriac Christian text, written in the late 4th or early 5th century CE.
It recounts the legend of the Image of Edessa as well as the legendary works of Addai and his disciple Mari in Mesopotamia.
[1] The story of how King Abgar and Jesus had corresponded was first recounted in the 4th century by the church historian Eusebius of Caesarea in his Ecclesiastical History (i.13 and iii.1) and it was retold in elaborated form by Ephrem the Syrian.
[citation needed] Helmut Koester regards the development of tradition of Thaddaeus' activity in Edessa as part of an effort to build the authority of the orthodox or Palutian[a] faction in Syria against the Manicheans and gnostics, who had an older and stronger presence in the area and traced their lineage to Thomas the Apostle.
[2][b] He considers the Palutian faction to have come to Edessa around 200 CE and only become significant in the fourth century.