With the unification of the Anglo-Saxon kingdoms (outside the Danelaw) by Alfred the Great in the later 9th century, the language of government and literature became standardised around the West Saxon dialect (Early West Saxon). Alfred advocated education in English alongside Latin, and had many works translated into the English language; some of them, such as Pope Gregory I's treatise Pastoral Care, appear to have been translated by Alfred himself. In Old English, typical of the development of literature, poetry arose before prose, but King Alfred the Great (871 to 901) chiefly inspired the growth of prose.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): When did Alfred the Great's reign begin?
871