Ennius 550 Sk (atque atque accedit muros Romana iuventus, ‘The Roman youth atque atque advanced against the walls’) has long puzzled scholars on account of what appear to be side-by-side tokens of the conjunction atque ‘and’. In this paper, I advance a new interpretation of this fragment. Atque in this fragment is a remnant of the precursor adverb from which the conjunction atque ‘and’ emerged. The adverb atque means ‘straightaway’ or ‘directly’ and when iterated has an intensified meaning, which Nonius correctly paraphrased long ago as “festine et intrepidanter.” This analysis not makes sense of the Ennean line, but also sheds light on cognates of atque found elsewhere in archaic Indo-European.