SummaryThis paper discusses how the notion of clock time was introduced in the Greek world. On the basis of an analysis of the earliest (potential) references to hours and clocks in texts from the late fifth to the early third century BC in their historical context, and with reference to the earliest archaeologically attested clocks, it proposes a scenario for the conception and development of this conventional system. It offers a new interpretation of the problematic passage Herodotus 2.109 and argues (...) that an hour-like unit was developed by late fifth century astronomers, under Babylonian influence, to denote the time in which a celestial body moves through a section of its diurnal circle. When this astronomical concept moved to the civic sphere in the second half of the fourth century, it changed from a scientific unit of duration to a civic unit for measuring the time of day. This shift probably took place in Athens, where the first references to hours appear in this period together with multiple experiments in clock making, as well as humorous reactions to the newfound sense of temporal precision. The paper will also show, however, that these first clocks did not yet tell seasonal hours – the type of hours that would eventually define Greco-Roman clock time – and still measured the lapse of time rather than enabling the location of moments in time. Greco-Roman clock time was only fully formed when it incorporated Egyptian notions of the hour in the Ptolemaic kingdom of the early third century BC. (shrink)