A medieval sword inscribed with a mysterious message is stumping researchers and causing a stir among armchair historians. The 13th-century weapon was found in the River Witham in Lincolnshire, in the United Kingdom, in 1825. It now belongs to the British Museum, but is currently on loan to the British Library, where it’s being displayed as part of an exhibit on the 1215 Magna Carta. The sword looks fairly ordinary at first glance. Weighing in at 2 lbs., 10 ounces (1.2 kilograms) and measuring 38 inches (964 millimeters) long, the weapon is steel, with a double edge and a hilt shaped like a cross. But on one side of the sword is a mysterious inscription, made by gold wire that has been inlaid into the steel, which reads, “+NDXOXCHWDRGHDXORVI+.