This article presents a comparative investigation of Herodotus and Sima Qian with a focus on their ethnographies of nomadic peoples. Both historians included geography and ethnography in their works because their societies had reached a stage when it was no longer possible to write their histories without taking the measure of their wider environment. The author posits that frontiers are not just locations of “othering” but also zones of creative interaction and regions in which it is possible to take the fi rst steps toward an appraisal of the rationality of foreign cultures. Herodotus and Sima Qian combined an incipient cultural relativism with notions of common humanity, resulting in an anthropological turn, the representation of the cultures of “others” as autonomous systems that must be judged on their own terms. Their anthropological turn is connected to their conceptions of empire and the temporalities underpinning their histories.