Archaeologists believe they have discovered the world's oldest lunar "calendar" in an Aberdeenshire field.

Excavations of a field at Crathes Castle found a series of 12 pits which appear to mimic the phases of the moon and track lunar months.

A team led by the University of Birmingham suggests the ancient monument was created by hunter-gatherers about 10,000 years ago.

An artist's impression of the site shows burning material in one of the "calendar's" pits.

The BBC's Huw Edwards spoke with Professor Vince Gaffney, an expert in landscape archaeology.