Late Roman Unit Sizes

[Renatus]

Ridley, as I see it, should have translated the number as it was in the text and then add Sozomenos' parallel in the footnote.

I do not know what edition of Zosimus you are using but the Internet Archive has Mendelssohn's 1887 Teubner edition in which the text has been emended to read 'chiliadon'. The apparatus includes the reference to Sozomen and gives the reading 'myriadon' from the manuscript V. It seems that as early as that philologists were emending the text to correct what appeared to be an obvious error.

"ἐτετάχατο δὲ ἐν τούτῳ Ἰοβιανοὶ καὶ Ἑρκουλιανοί· ταγμάτων δὲ ταῦτα ὀνόματα, παρὰ Διοκλητιανοῦ καὶ Μαξιμιανοῦ καταστάντα"

In it arrayed the Joviani and the Herculiani, these are names of tagmata, established by Diocletianus and Maximianus.

You may be able to explain a peculiarity of Ridley's translation. He ends 3.30.2 with " . . . where the Joviani and Herculani were posted." Then, in an asterisked footnote, he adds, "The names of these legions were given by Diocletian and Maximian: they bear their surnames Jovius and Herculius respectively." He does this sort of thing many times in his translation but there is no explanation that I can find of what these footnotes are. Possibly they come from another manuscript. Do you know?