Bardaisan (11 July 154 – 222 AD; ܒܪ ܕܝܨܢ, Bar Dayṣān), known in Arabic as ibn Dayṣān (ابن ديصان) and in Latin as Bardesanes, was a Syriac-speaking Assyrian Christian writer and teacher with a gnostic background, and founder of the Bardaisanites.
A scientist, scholar, astrologer, philosopher, hymnwriter, and poet, Bardaisan was also renowned for his knowledge of India, on which he wrote a book, now lost. According to the early Christian historian Eusebius, Bardaisan was at one time a follower of the gnostic Valentinus, but later opposed Valentinian gnosticism and also wrote against Marcionism.
Bardaisan (ܒܪ ܕܝܨܢ bar Daiṣān "son of the Dayṣān") was a Syriac author born on 11 July 154 in Edessa, Osroene, which, in those days, was alternately under the influence of both the Roman Empire and the Parthian Empire. To indicate the city of his birth, his parents called him "Son of the Dayṣān", the river on which Edessa was situated. He is sometimes also referred to as "the Babylonian" (by Porphyrius); and, on account of his later important activity in Parthian Armenia, "the Armenian", (by Hippolytus of Rome), while Ephrem the Syrian calls him "philosopher of the Arameans" (ܦܝܠܘܣܘܦܐ ܕܐܖ̈ܡܝܐ). Some sources refer to his high birth and wealth; according to Michael the Syrian, Bardaisan's parents had fled Persia and Sextus Julius Africanus reports that he was of the Parthian nobility. His parents, Nuhama and Nah 'siram, must have been people of rank, for their son was educated with the crown-prince of Osroene at the court of Abgar VIII. Africanus says that he saw Bardaisan, with bow and arrow, mark the outline of a boy's face with his arrows on a shield which the boy held.
Owing to political disturbances in Edessa, Bardaisan and his parents moved for a while to Hierapolis (now Manbij), a strong centre of Babylonianism. Here, the boy was brought up in the house of a priest Anuduzbar. In this school he learnt all the intricacies of Babylonian astrology, a training that permanently influenced his mind and proved the bane of his later life.