Archaeologists believe they have discovered the world's oldest "calendar" in a field in Scotland.
New analysis of a group of 12 pits excavated in Aberdeenshire shows they appear to mimic the phases of the moon to track lunar months over the course of a year.
Until now the first formal time-measuring devices were thought to have been created in Mesopotamia about 5,000 years ago.
But the pit alignment near Crathes Castle predates those discoveries by thousands of years, experts say.
The Mesolithic monument at Warren Field is said to have been created by hunter-gatherer societies nearly 10,000 years ago.
It was excavated between 2004-06 and recently analysed by a team led by the University of Birmingham.
They found the monument also aligns on the Mmidwinter sunrise, which researchers say would provide an annual "astronomic correction" to maintain the link between the passage of time indicated by the moon, the solar year and the seasons.
The project was led by Vince Gaffney, professor of landscape archaeology at the University of Birmingham.
He said: "The evidence suggests that hunter-gatherer societies in Scotland had both the need and sophistication to track time across the years, to correct for seasonal drift of the lunar year and that this occurred nearly 5,000 years before the first formal calendars known in the near east.
"In doing so, this illustrates one important step towards the formal construction of time and therefore history itself."
Dr Richard Bates, from the University of St Andrews, was also involved in the project and said the pit monument provided new evidence of the "sophistication" of societies in early Mesolithic Scotland.
"This is the earliest example of such a structure and there is no known comparable site in Britain or Europe for several thousands of years after the monument at Warren Fields was constructed," he said.
The pit site was first discovered when unusual crop markings were noticed during an aerial survey by the Royal Commission on the Ancient and Historical Monuments of Scotland.
It lies on the National Trust for Scotland's Crathes Castle estate and was excavated by the trust and Murray Archaeological Services.
Dr Shannon Fraser, the trust's archaeologist for eastern Scotland, said: "This is a remarkable monument which is so far unique in Britain.
"Our excavations revealed a fascinating glimpse into the cultural lives of people some 10,000 years ago - and now this latest discovery further enriches our understanding of their relationship with time and the heavens."
The research was published in the journal Internet Archaeology today.