The phrase Ἐν ἀρχῇ ἦν ὁ λόγος is the first verse from John, chapter 1, and is commonly translated as "In the beginning was the Word". I would like to know why the definite article is missing inside the prepositional phrase, Ἐν ἀρχῇ. I would expect to see Ἐν τῇ ἀρχῇ instead. Is there some rule I am unaware of pertaining to articles inside prepositional phrases? Or is there some more general rule pertaining to the omission of definite articles that explains this phrasing?
Part of my confusion stems from the fact that almost every English translation I have read renders it as a definite noun. But perhaps Ἐν ἀρχῇ was idiomatic at the time, and did not require an article. It would be nice to know, additionally, whether this phrase was grammatical in both Attic and Koine, or only the Koine dialect. If it was common in Attic, then any examples from Attic texts would be much appreciated.
Thank you in advance for any feedback.