This strange lunar-like landscape in the middle of Thetford Forest in Norfolk, England, looks very similar to mortar craters in Normandy and in Somme from the First World War. But these ones in Norfolk have a different origin, and despite their name, they are not graves. Grime's Graves is actually a large flint mining complex from the Neolithic age that’s at least 4,500 years old.

In the Neolithic era, flint —a hard, mineralized form of quartz—was a valuable natural resource and highly prized because of its tendency to break into thin flakes with a razor sharp edge that was very useful to make tools and weapons. Indeed, flint remained in use for many centuries even after men learned to make tools out of metals.

Photo credit: www.english-heritage.org.uk