The oldest calendar known to exist was created some 5,000 years ago in Mesopotamia—but it's looking positively youthful in the face of a new find in northern Scotland. A dig at Warren Field in Aberdeenshire in 2004 is just now giving up its secrets, with archaeologists revealing that a series of 12 pits found there may in fact be the world's oldest calendar. They believe the Stone Age-era pits each acted as a stand-in for a calendar month, with the 12 collectively representing a year. Additionally, the pits may have collectively represented a single lunar month, and their varied depths in the 165-foot arc-shaped row indicate that time period was split into what the Independent calls three "weeks"—waxing, full, and waning.
The Australian calls out two notable aspects of the pits: For one, Scotland's prehistoric hunter-gatherer tribes have long been considered "civilization's late starters"; the find somewhat unravels that belief. Second, their calendar took into account "lunar drift"; because lunar months don't precisely align with the passage of a year, most early calendars tracked only the former. But these pits would have been able to reveal the arrival of the midwinter solstice and, with it, the year's end, a further indication of the people's sophistication. A neat side note from the BBC: The Warren Field site was identified as one worth investigating via odd crop marks seen from above by the country's Royal Commission on the Ancient and Historical Monuments. (Read more calendars stories.)