My subject is the history of science in antiquity, where the convention I adopt for “antiquity” is that it covers everything from the earliest recorded Mesopotamian investigations in the third millennium BCE down to the end of the third century CE, by which time two particularly significant upheavals had taken place at either end of the Euro-Asia land mass. I refer to the Christianization of the Greco-Roman World and the rise of Buddhism in China. That study poses a number of distinctive problems, both substantive and methodological, which I shall go on immediately to identify. At the same time it is particularly worthwhile, in my view, for the light it can throw on very early efforts at understanding the physical world. Let me give a brief preliminary explanation of my main thesis.