How Did First-Century Jews Keep Time at Night?

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The Jews of the first century C.E. did not have mechanical clocks or modern timekeeping devices, yet they possessed and inherited systems of telling time that were both practical and sophisticated for their context. During the daylight hours, sundials could be used to determine time, as the movement of the sun cast shadows on a calibrated surface. However, sundials were of no use during cloudy weather or at night. To track time after sunset, first-century Jews—like many surrounding cultures—relied on a clepsydra, or water clock, a method borrowed and refined from earlier civilizations including the Egyptians, Persians, Greeks, and Romans.

The Clepsydra (Water Clock)

The clepsydra (from the Greek kleptein, “to steal,” and hydōr, “water”) literally means “water thief,” and it measured time by the regulated flow of water. This instrument operated by allowing water to flow either:

Out of one vessel into another through a small aperture, or
Into a vessel from another, depending on the design.

Both the upper and lower containers could be marked with gradations, allowing the viewer to determine how much time had passed by observing the changing water level.

According to The Jewish Encyclopedia, the Mishnah and the Talmud refer to the clepsydra under several terms, possibly reflecting various models or adaptations of the device. Regardless of name or form, all variants functioned by measuring time through the slow, steady release of water, drop by drop—a reliable way to track time especially during the night hours.

Biblical and Historical Context for Timekeeping

The Bible does not directly reference the clepsydra by name, but the Jewish division of time into watches implies the need for some kind of mechanism or marker to designate these periods.

During the time of Jesus and the Roman occupation, the Jews adopted the Roman four-watch system to divide the night. This system divided the twelve hours of darkness into four three-hour intervals, typically understood as follows:

Evening – Sunset to around 9:00 p.m.
Midnight – About 9:00 p.m. to midnight
Cockcrow – Midnight to about 3:00 a.m.
Morning – 3:00 a.m. to sunrise

This framework is reflected in Mark 13:35, where Jesus warns:

“Be on the alert then, for you do not know when the master of the house is coming, whether in the evening, at midnight, at cockcrow, or in the morning.”

To maintain this timing accurately, Roman military outposts used water clocks to signal the changing of the guard. A trumpet blast would accompany each watch change, serving as an audible cue to those nearby—soldiers and civilians alike. This would allow Jews living under Roman rule, especially those in proximity to Roman camps or cities, to stay synchronized with official time divisions.

Cultural Continuity and Utility

The clepsydra was not merely a Roman tool. The widespread use of water clocks across ancient civilizations—including among Jews—demonstrates their functional utility and adaptability. Although the technology was simple, it was sufficiently accurate for purposes such as:

Dividing the night into watches for guard duty or religious observance
Temple service timing, including specific periods for prayers or offerings
Community awareness of significant periods (e.g., Sabbaths, festivals, or Passover observances beginning at sunset)

The fact that rabbinic texts mention the clepsydra under various names suggests that it was familiar enough to warrant linguistic and technical classification. Furthermore, it highlights the Jewish engagement with broader Greco-Roman scientific and technological practices, adopting them as necessary to maintain orderly communal and religious life.

Conclusion

First-century Jews kept time at night through the use of the clepsydra, or water clock—a widely used ancient device that functioned by measuring the flow of water between vessels. The adoption of the Roman four-watch night division necessitated practical means of tracking these periods, especially during times of darkness. In Roman camps, trumpet blasts accompanied the change of the watch, and this likely served as a community-wide auditory cue. This system enabled Jews to honor religious timings, maintain order, and remain vigilant in a world where God’s commands and temporal discipline were closely linked. Although seemingly primitive by modern standards, these methods illustrate the ingenuity and adaptability of God’s people in their pursuit of obedience and structure.

About the Author

EDWARD D. ANDREWS (AS in Criminal Justice, BS in Religion, MA in Biblical Studies, and MDiv in Theology) is CEO and President of Christian Publishing House. He has authored over 220+ books. In addition, Andrews is the Chief Translator of the Updated American Standard Version (UASV).