Roman Timekeeping

Roman timekeeping divided the day into two parts, then into twelve variable-length hours based on daylight, with winter hours about 45 minutes and summer hours about 75 minutes. The civil day ran from midnight to midnight, while the natural day ran from sunrise to sunset, and Romans used sundials, later calibrated by water clocks, to measure time. The system influenced later terms such as “siesta,” “noon,” and the Catholic canonical hours.