Groovy

http://commons.wikimedia.org/wiki/File:Misrah_Ghar_il-Kbir_5.jpg
Image: Wikimedia Commons

Malta is criss-crossed with ruts like these. No one knows who made them, when, or why. If they’re cart ruts, why are some 60 centimeters deep? If it’s an irrigation system or some kind of astronomical undertaking, what was its purpose?

The most popular theory is that ancient sledges hauled limestone to build local temples. But why then do some ruts lead straight into the sea?