Although they did not fix their schedules to the clock in the modern sense, ancient civilizations adjusted daily schedules to the sun more flexibly than modern DST does, often dividing daylight into twelve hours regardless of day length, so that each daylight hour was longer during summer. For example, Roman water clocks had different scales for different months of the year: at Rome's latitude the third hour from sunrise, hora tertia, started by modern standards at 09:02 solar time and lasted 44 minutes at the winter solstice, but at the summer solstice it started at 06:58 and lasted 75 minutes. After ancient times, equal-length civil hours eventually supplanted unequal, so civil time no longer varies by season. Unequal hours are still used in a few traditional settings, such as some Mount Athos monasteries and all Jewish ceremonies.

What kind of clocks did the Romans use?