Heteirarcha, in antiquity, an officer in the Greek empire, whereof there were two species; the one called simply Heterarch, and the other great heterarch, who had the direction of the former.

The word is Greek, ἱστιαῖος, formed of the Greek ἱστιαῖος, σοιοῦς, "companion, ally," and ἰστιαῖος, imperium, "command." Their principal function was to command the troops of the allies; besides which, they had some other duties in the emperor's court, described by Codin, De Officiis, cap. 5, No. 30, 31, 32, 37.