What is Time? Ancient Calendars

Every ancient culture made accurate measurements of celestial motion, but they had a range of different solutions to the conflict between the lunar and solar year.

Lunar Calendars

Twenty thousand years ago, Ice Age hunters scratched lines and holes in bones to show the days before the next new moon. The discovery of an eagle bone at le Placard, dated to 13,000 BC, is one of the earliest examples of humankind recording itself against natural phenomenon. Similar observations were made by ancestors of each of the ancient civilisations, but as they approached 5000 BC, their understanding of astronomy led them all to note the differences between lunar and solar time, and to find ways of catching up periodically.

Cultures of the Tigris and Euphrates

time, calendar, ancient calendar,Some written records exist from these ancient cultures, although much has been lost, particularly from the Babylonians (whose methods and mythology prefigured much in the Christian Bible), due to great fires at the libraries of Alexandria in 97 BC and AD 696. We do know, at least, that their lunar year, before 2000 BC, consisted of 12 months of alternating 29 and 30 days. The Sumerians, their predecessors, rounded the lunar month up to 30 days, giving them 360 days every year, which neatly dovetailed with their base 60 numbering system, (which formed the basis of the imperial system of 12 inches in a foot and 24 hours in a day).

Solar Years

Some evidence of time notation remains in the form of artifacts. Stonehenge, for instance, is an incredible formation of standing stones which, whatever its other pur­poses, perfectly records the summer solstice, designed so the sun shines down the central avenue, illuminating the centre stone.

Archeological finds and early documents have revealed that the ancient Greeks added 90 days every eight years to make up the difference between the lunar and solar years. The Chinese, by c. 2350 BC, had added seven months every 19 years. Jewish astronomers added one month every three years with a further month added by decree when necessary.

Unusually, the Mayans of Central America used a solar year of 365 days, with 18 months of 20 days each and a further five special days. In fact, they also had another calendar of 260 days, a cycle reserved for days of worship. Using this – combined with the 365-day calendar – they calculated what they termed Calendar Rounds. Separately they measured Long Cycles of 360-day units called tuns, which they multi­plied by 400 then 13 to create their Great Cycles of 5130 years which marked the end of one life and the start of another. The end of the current cycle, the end of the world according to Mayan predictions, was AD 2012.

What is Time?

The Ancient Egyptians

The ancient Egyptians are especially important to our concept of time because their intellectual and cultural in­fluence had a major impact on the development of the Julian calendar, leading to the Gregorian form we use today.

The Nile, as the source of life, was also the key to the Egyptian understanding of time. Using a nileometer, possibly as early as 5000 BC, they determined that the year was 365 days long. The nileometer had notches or steps in the banks of the Nile marking the different levels of water height from the low point in May to its highest in September, so they could plan for the floods between June and October, the planting and growth of crops from October to February and the harvest from February to June. The shadows cast by the pyramids were also used to measure equinoxes, in a similar way to the menhirs of Stonehenge.

The ancient Egyptians’ advanced pursuit of knowledge led them to observe that the star we know as Sirius rose in line with the sun at the point every year when the annual inundation of the Nile occurred. This enabled them to conclude that the year was in fact 365 1⁄4 days long.

In a move which has echoes throughout the history of time, however, local priests resisted this slight change, having adopted the 365-day year as sacred, even though scientific observation proved them to be incorrect. The priests saw science as undermining their authority, a theme we’ll encounter again in Europe’s Dark and Middle Ages.


time, calendar, ancient calendar, Egypt, AlexandriaBy 334 BC, Alexander the Great (356–323 BC) had conquered Greece, Egypt and Persia – three of the most literate, philosophically and scientifically inclined nations in the world. The knowledge from these three cultures was brought together in the cosmopolitan Egyptian city of Alexandria, built by Alexander in 332 BC. This metropolis, with its population of 300,000 (not counting slaves) by the first century AD, also housed the most extensive library of the world’s great literature, including Aristotle’s works. Waterclocks were created here, an encyclopedia of astronomy was drawn up, mathematical treatises and musings on the nature of time and man were distributed.

It is possible to trace the origins of all core principles behind the measurement of time (and the calendar) to the astronomical and mathematical scholarship of Alexandria in the two centuries before the birth of Christ and beyond.

Caesar and Cleopatra

Shakespeare’s dramatic Cleopatra (69–30 BC)seems to have been an accurate portrayal of the intelligent, passionate, politically sagacious historic figure who seduced Julius Caesar (100–44 BC) in order to remove her brother Ptolemy from the steward­­ship of an Egypt which had by been conquered by the Roman Empire.

Caesar was a powerful military and political leader, whose success had given him power over the whole of Europe, North Africa and the Middle East: more than half the known world of the time. The chaos and dispute of dates throughout the vast Empire made Caesar determined to bring the calendar under his authority: it is said that in 47 BC, at a feast arranged by Cleopatra to honour Caesar, he discussed the Egyptian method of measuring the year with the celebrated astronomer Sosigenes and decided how to effect a far-reaching reform of time.

The next Time post looks at the Julian Calendar which was used in the West until 1582, by which time 13 days had been lost! So Christmas, Easter, the Summer Solstice and more were celebrated at the wrong time…

Some other posts of interest.

The image in the head of this post is the  Aztec calendar stone, from 15th Century, now housed at the National Anthropology Museum in Mexico City (see here for a good article)

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