How Did the Romans Tell Time?

The Romans told time by sundials and water clocks in daylight and by water clocks alone at night, dividing the period from sunrise to sunset into twelve unequal hours whose length shifted with the season. The longer reckoning — the calendar of kalends, nones, and ides — counted days within each month under a 355-day lunar cycle that was repeatedly corrected by the pontiffs until the reform of Julius Caesar fixed the year at 365 days with a leap day every four years. Both systems coexisted: the hora for the practical business of the day, and the kalendarium for the religious, civic, and legal life of the state. For a fuller sense of how time structured the day, see Roman society and daily life.

Sundials: The Hours of Daylight

The earliest known Roman sundial (solarium) was brought to Rome from Sicily in 264 BCE and set up in the Roman Forum by the consul Marcus Valerius Messalla. It was, however, ill-suited to the Roman latitude, and for nearly a century Romans continued to set civic business by the informal announcement of the praeco from the Rostra at first light, midday, and sunset. By the second century BCE Greek horologium design had entered Roman use, and by the first century BCE every sizeable city in the Roman world sported at least one public sundial — the Horologium Augusti in the Campus Martius, a vast bronze obelisk brought from Heliopolis in Roman Egypt and erected by the emperor Augustus in 10 BCE, cast a shadow across a great marble paving in such a way that the time of day could be read from inscribed lines.

A sundial’s hour, however, was not the modern equal hour. Romans divided daylight into twelve horae regardless of the time of year: in summer an hora could be roughly 75 modern minutes, in winter only about 45. This is why Plautus, writing in the second century BCE, jokes about lawyers overcharging by reading the time in summer hours and undercharging in winter. The hour of midday was called meridies, the sixth hour of daylight; noon, in the modern sense, was prima hora in summer and tertia in winter.

Water Clocks: The Hours of Night

Because sundials failed at night and on cloudy days, the Romans developed the clepsydra, or water clock. A clepsydra was a stone or bronze vessel with a small hole near the base, from which water dripped at a roughly constant rate. Markers on the inner wall divided the descending water level into horae. The most famous Roman clepsydra was the Horologium Water Clock of Roman Britain, recovered from a tomb in the late 19th century and now in the British Museum. The simpler, smaller versions were used in law courts: the consul or praetor held a button and released the water, and when the level reached a marked line the lawyer’s time was up. Cicero complained bitterly in his speeches that his opponents had asked for an unfair clepsydra — one that had not been reset since the previous speaker.

The Roman Calendar: Kalends, Nones, and Ides

The Roman civil calendar, traditionally attributed to Romulus and refined by Numa Pompilius, was a 355-day lunar cycle with twenty-nine or thirty-one day months and an additional twenty-two day intercalary month, Mercedonius, inserted periodically to keep the calendar in step with the seasons. The pontiffs, who controlled intercalation, kept adding or skipping these extra months for political reasons — shortening the term of a hostile consul, lengthening a friendly one’s — so that by the late Republic the calendar was running months ahead of the actual seasons. Dates were not given as numbers of the month, but counted backward from three fixed points: the kalendae (the first of the month), the nonae (the fifth, or the seventh in March, May, July, and October), and the idus (the thirteenth, or the fifteenth in those same four months). Thus ante diem III Kalendas Apriles meant “the third day before the kalends of April” — that is, March 30. Inscriptions on Roman tombstones and acts of the Senate used this counting system, and the formula remained in use for centuries, well into the Christian era.

The Julian Reform

In 46 BCE, Julius Caesar, advised by the Alexandrian astronomer Sosigenes, carried out the most famous calendar reform in Western history. The year of confusion, annus confusionis, ran to 445 days, and the new year 45 BCE, the year of the Julian calendar, established a 365-day year of twelve months with a leap day every four years. Caesar also renamed Quintilis to July in his own honor, and his adopted son Augustus later renamed Sextilis to August in turn — though Augustus had to steal a day from February to give August thirty-one days, which is why the months of the modern calendar alternate so awkwardly. To learn more about the man behind the reform, see the biography of Julius Caesar and Augustus Caesar. The Julian calendar would reign in Europe for sixteen centuries, until the Gregorian reform of 1582.

The Week, the Nundinae, and Religious Time

The Romans did not have a seven-day week in the modern sense. Their basic cycle of rest was the nundinae, a market day that recurred every eight days by inclusive Roman counting (the modern nine-day week). The seven-day week entered the Roman world only in the late Empire, with the spread of Christianity and of Mithraism and other eastern cults that had inherited the planetary week from Babylonian astrology. The planets — Saturn, Jupiter, Mars, Sol, Venus, Mercury, Luna — gave the seven days their Latin names, which survive in modern Romance languages: dies Solis, dies Lunae, dies Martis, dies Mercurii, dies Iovis, dies Veneris, dies Saturni. The Latin word calendar itself comes from kalendae, the day when debts were traditionally announced and the calator was sent to collect them. The Vestal Virgins, who maintained the sacred flame and the religious calendar, were the keepers of public time; learn more about them in Who were the Vestal Virgins?.

The Year of the City

Roman citizens did not number years the way we do, from a fixed zero point. Instead, they counted years from the legendary founding of the city — ab urbe condita, AUC. The traditional year of the foundation, set by Marcus Terentius Varro, was 753 BCE. Thus the Augustan settlement of 27 BCE was known in Roman sources as year 726 AUC, and the age of the great orator Cicero ran from year 648 to 711 AUC. This system of dating, recorded by Livy, Tacitus, and Pliny the Elder, is still used by classical scholars today, alongside the modern BCE/CE system, and it remains the dignified way of marking Roman time.