You may have spotted these strange concrete blocks dotted around our verdant countryside and pondered their purpose. Nothing to do with an alien landing force I'm afraid, they're actually WWII anti-tank devices or dragon's teeth.
Designed to impair the advancement of invading tanks and armoured vehicles, the blocks were positioned to channel the invaders into accessible areas for easier attack. Land mines and barbed wire were placed between the teeth to slow foot soldiers. Nice.
In Germany, the Siegfried Line is a defensive barrier that ran for over 390 miles from the Swiss to the Dutch border. Along with thousands of tunnels and bunkers, there was a very high unknown number of dragon's teeth, many of which remain today.
Dragon's teeth are to be found globally in many shapes and guises, some still with their intended use. In Switzerland they are often called Toblerone lines – I wonder why?
Hover over or click the image for their location.