Empires have occasionally been described as vast redistributive systems, drawing goods into the centre and pumping them out to the peripheries not just material goods, but people too. And with the human ebb and flow moved information, some more and some less reliable. A little of it was predigested, in the form of local histories penned on the middle ground….. There were no great officially sanctioned surveys like those through which we know India under the British Raj, and no scientific papers like those of Joseph Banks. The great mass of information must have been less organized, travellers tales and the like. Of the vast quantity brought in each generation, most was lost. But while it was in circulation it might be harvested. A Polybius or a Strabo might, if he wished, join the circulation of warm bodies for a while, and get a sense of the flow. But it was sufficient to stand at the right points of the system and gather ethnographic knowledge as it passed by, like a coral polyp fixed on some reef, selecting titbits and rejecting others from the rich currents, according to some prior design.
Greg Woolf, Tales of the Barbarians: Ethnography and Empire in the Roman West