The Warren Field Calendar is an archaeological excavation discovered in the Dee River Valley of Aberdeenshire, Scotland, in 2004. It was not until 2013, however, that the find was discovered to be the world’s oldest known calendar, dating back over 10,000 years.
The Mighty Mesolithic Monument of Aberdeenshire
Warren Field is located near Crathes Castle in Aberdeenshire county, in northeastern Scotland. The field itself contains a series of a dozen purpose-dug pits that are believed to correspond to the twelve phases of the Moon, as in a lunar calendar. It was discovered from the air by the Royal Commission on the Ancient and Historical Monuments of Scotland and first excavated in 2004.
The twelve pits are shaped to mimic the phases of the moon, and appear to be intended to help the observer track lunar months. The pits align along the southeastern horizon, and with sunrise on the day of the Winter Solstice. This provides annual astronomical corrections to coordinate the solar year with the lunar cycles, and helps account for the asynchronous solar year (which is why we need Leap Day every four years).
The Warren Field Calendar may also have been used as a seasonal calendar to help nearby communities of the age track the migration of animals they hunted for sustenance. The fact that it was created by a society of hunter-gatherers, rather than farmers, is unique amongst historically significant ancient calendars.
Evidence indicates that the pits were carefully maintained and repeatedly reshaped in response to shifting solar and lunar cycles; the monument may have been altered hundreds of times over the 6,000 year period in which it was used.
For whatever reason, the Warren Field Calendar fell out of use approximately 4,000 years ago. The find has been dated to roughly 8000 BCE, during the Mesolithic Period (circa 10,000 to 5000 BCE). Thus, the Warren Field Calendar predates the next-oldest historically-known calendars, from Mesopotamia, by over 5,000 years.