Mars & Asteroid Belt Agrogram

This Agrogram clearly depicts the inner solar system with Mars excluded, perhaps to highlight mars as the point of interest being the large central circle itself. There is an outer belt of asteroids which could be the asteroid belt or could indicate a Mars planetary cycle of some kind, perhaps the Martian moon. Appeared near Windmill road in Kemble, Glouscestershire, interestingly not far from the source of the river Thames.