High Quality Content by WIKIPEDIA articles! 366 geometry or 366-degree geometry (also called megalithic geometry) is the name given to an hypothetical geometry supposedly used and perhaps created by an alleged megalithic civilization of Britain and Brittany, France, according to British authors Alan Butler and Christopher Knight, and French author Sylvain Tristan. This geometry, whose origin is claimed to go back to c. 3500 BC, would have used a 366-degree circle rather than a 360-degree circle as we do today.