The Christians were generally designated as atheoi, as deniers of the gods, and the objection against them was precisely their denial of the Pagan gods, not their religion as such.

from ATHEISM IN PAGAN ANTIQUITY,A. B. DRACHMANN, PROFESSOR OF CLASSICAL PHILOLOGY IN THE UNIVERSITY OF COPENHAGEN, GYLDENDAL, 1922

oh, the ironing.

(Atheism in pagan antiquity on Archive.org. H/t to Nullifidian’s post: Britain’s First Newe Atheiste for directing me to the delights of archive.org)