A mysterious series of Bronze Age carvings — depicting three processions of gods walking towards two supreme deities — may have been a most surprising calendar.

Markers under each line of gods would have been used to keep track of the lunar days, the months and a third, 19-year cycle that was part of a calendar correction.

Every 19 years an extra month would be added to the calendar in the so-called Metonic cycle in order to keep pace with the solar year.

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A mysterious series of Bronze Age carvings — depicting three processions of gods walking towards two supreme deities — may have been a most surprising calendar

WHO WERE THE HITTITES? The Hittites were an ancient Anatolian people whose empire lay in what is today Turkey. They lived between 1600–1180 BCE. Hittite domestication of horses allowed them to both travel and migrate over long distances. Conflict between the Hittites and the Ancient Egyptians eventually led to the earliest recorded example of a peace treaty. The Hittites followed a polytheistic religion in which the storm gods were especially prominent. Advertisement

During the Bronze Age, the city of Hattusa — located in what is today northern Turkey — was the capital of the Hittite empire and home to assorted temples, royal residences and types of fortification.

Lying a few kilometres north-east of the city is the remains of a mysterious ancient religious sanctuary experts have dubbed 'Yazılıkaya', or 'inscribed rock', which lies atop a large limestone outcrop.

Both Hattusa and Yazılıkaya have been designated UNESCO world heritage sites, the latter for its high-quality rock carvings, which have earnt the site a reputation as being the 'Sistine Chapel' of Hittite religious art.

The rock art appears in a roofless limestone chamber, on the prominent northern wall of which features depictions of the sun-goddess Hebat and the storm-god Teshub, the supreme deities of the Hittite pantheon.

On the east and west walls on either side of the chamber, lesser carved deities march in two processions towards Hebat and Teshub.

Researchers have proposed that the Hittite people used the carvings as a form of calendar, moving stone markers back and forth along benches beneath the carvings in order to keep track of the progression of time.

'Yazılıkaya has an aura to it,' Eberhard Zangger, paper co-author and president of the international non-profit foundation Luwian Studies, told the New Scientist.

'Part of it is because it’s an unsolved enigma, part of it is the beauty of the place.'

The procession of carved gods on the western wall fall into two groups, one containing 12 figures and the other 30.

Meanwhile, the eastern wall sports 17 deities, but Dr Zangger and his colleague Rita Gautschy, an ancient historian from the University of Basel in Switzerland, have suggested that once there were two more, based on engravings and gaps in the procession.

The researchers propose that the numbers of these gods — 30, 12 and 19 — the first two corresponding to the lunar cycle and the passing months.

Markers under each line of gods would have been used to keep track of the lunar days, the months and a third, 19-year cycle that was part of a calendar correction

As each time period elapsed, the Hittites would have moved the corresponding marker, the researchers argue — likely back down the procession, in keeping with the way in which these hieroglyphs are read.

These two counts alone are not sufficient to make an accurate calendar, however, as 12 lunar months is just under 11 days short of a solar year, calling for two corrections.

Firstly, the addition of an extra, or 'intercalary' 13th month every three years serves to bring the calendar into rough alignment with one Earth revolution about the sun.

The final measure to stop this kind of calendar from drifting is to add one more intercalary month every 19 years — following the so-called Metonic cycle.

Drs Gautschy and Zangger believe the Hittites used the final procession of 19 carved gods to track progress through the Metonic cycle and work out when to add the crucial extra month every 19 years.

Every 19 years an extra month would be added to the calendar in the so-called Metonic cycle in order to keep pace with the solar year

While ancient texts reveal that calendars using intercalary months every three years date back to around two millennia before Yazılıkaya, it was thought that calendars using the more intricate Metonic cycle were not invented for another 700 years.

'We would probably not expect knowledge of the 19-year cycle in the 2nd millennium BCE,' Dr Gautschy told New Scientist, suggesting that, if the carvings were a calendar, the Hittites must have had considerable astronomical knowledge.

'It’s not only a striking idea, it’s reasonable and possible,' Juan Antonio Belmonte of the Institute of Astrophysics of the Canary Islands, Spain — who wasn’t part of the work — told the New Scientist.

Professor Belmonte had previously shown that many Hittite buildings were lain out as so to align with important astronomical events, such as the summer solstice.

He commends Drs Gautschy and Zangger for noticing that the Yazılıkaya deities may have been used to follow a Metonic calendar cycle.

'I had this in front of my eyes and I was unable to see it,' he said.

Both Hattusa and Yazılıkaya have been designated UNESCO world heritage sites, the latter for its high-quality rock carvings, which have earnt the site a reputation as being the 'Sistine Chapel' of Hittite religious art

'The numbers in play — 12, 30 and 19 — are astronomically suggestive,' Edwin Krupp, director of the Griffith Observatory in Los Angeles told New Scientist, cautioning that this is not proof the site served as a calendar.

He also notes that the site's use to track Metonic cycle is dependant on the third wall having original contained two extra deities, which is another uncertainty.

Furthermore, Dr Krupp argued that the fact that many of the deities have their names carved underneath them would suggest that each god had an association with a day or month respectively — a notion not supported by known Hittite texts.

Similarly, University of Reading classicist Ian Rutherford told New Scientist that the texts have little to suggest the Hittites were interested in the sky above them at all.

'That may have something to do with the climate: it rains a lot in the Anatolian highlands,' he said, meaning the sky would often have been blocked off by cloud.

The rock art appears in a roofless limestone chamber, on the prominent northern wall of which features depictions of the sun-goddess Hebat and the storm-god Teshub, the supreme deities of the Hittite pantheon

In contrast, Dr Zangger believes that this places too much emphasis on written texts.

'Hittite society consisted of more than is reflected in the documents,' he said.

'Perhaps the carvings really are just gods walking in a certain sequence — but there seems to be so much more to it.'

The full findings of the study were published in the Journal of Skyscape Archaeology.