Anchor Stone Blocks were invented in the 1870s by two brothers, Otto and Gustav Lilienthal, who wanted a building toy that behaved like real masonry. They could not sell it, and in 1880 sold the rights to Friedrich Adolf Richter in Rudolstadt, who could. Otto Lilienthal went on to become one of the first people to fly.

The stones are still made to the original formula of quartz sand, chalk and linseed oil, and to the same dimensions, so a set bought today fits with one from a century ago. They hold together by weight and friction alone, with nothing to interlock, which is why a tower built from them stands the way a real one does.

Made in Rudolstadt by a company owned by a local workers' welfare association. Einstein had a set as a child.