This 13th-century double-edged sword, possibly of German manufacture, was found in the River Witham, Lincolnshire, in 1825. Inlaid in gold wire along one of its edges is a curious inscription:

+NDXOXCHWDRGHDXORVI+

It’s been speculated that this is a religious invocation, but its full meaning is not clear. In 2015 the British Library invited readers to offer their thoughts, but no conclusive solution was reached. Medieval historian Marc van Hasselt of Utrecht University says it may be the product of a sophisticated workshop that made swords for the elite, as similar blades have been found throughout Europe. “These similarities go so far as to suggest the same hand in making the inscriptions. However, their contents are still a mystery, regardless of their origins.”