Tatian of Adiabene, or Tatian the Syrian or Tatian the Assyrian, (/ˈteɪʃən, -iən/; Latin: Tatianus; Ancient Greek: Τατιανός; Classical Syriac: ܛܛܝܢܘܣ; c. 120 – c. 180 AD) was an Assyrian Christian writer and theologian of the 2nd century.
Tatian's most influential work is the Diatessaron, a Biblical paraphrase, or "harmony", of the four gospels that became the standard text of the four gospels in the Syriac-speaking churches until the 5th-century, after which it gave way to the four separate gospels in the Peshitta version.