Sentence:  The date of the Disputation itself admits of tolerably exact settlement. Epiphanius, indeed, says that Manes fled into Mesopotamia in the ninth year of the reign of Vaerianus and Gallienus, and that the discussion with <WSD>Archelaus</WSD> took place about the same time. This would carry the date back to about 262 A.D. 
Meaning of the word marked with <WSD> tags:  A bishop of Mesopotamia under the emperor Probus, noted for his treatise on the Manichaean heresy dating to AD 277.