Roman Timekeeping

Roman timekeeping divided daily life into two overlapping schemes: a civil day that ran from midnight to midnight and a natural day that ran from sunrise to sunset. Daylight was split into twelve horae whose length changed with the seasons and latitude - at Mediterranean latitudes an hour could be about 45 minutes at the winter solstice and about 75 minutes at the summer solstice. Romans named many parts of the civil day (media nox, meridies, vespera, crepusculum, etc.) and recorded events such as births by the civil day, while daylight hours were numbered hora prima, hora secunda, hora tertia, and so on, often qualified as diei or noctis to indicate day or night hours.

Time was measured with sundials and water clocks. A Greek sundial captured from the Samnites was set up in Rome around 293-290 BC, another came from Sicily in 263 BC, and the city’s first dedicated sundial was built in 164 BC. Sundials required sunshine and seasonal/latitudinal recalibration, so they were commonly used to calibrate water clocks that worked continuously. Elements of Roman practice survive in language and liturgy: Spanish siesta comes from sexta hora; the Church’s prime, terce, sext and none mirror Roman hours; noon derives from the ninth hour (originally 3 pm) and the a.m./p.m. distinction persists in 12-hour time.