In our modern life, we don't encounter swords much outside of the movie screen. For thousands of years, however, they were the pinnacle of weapons technology (and often non-weapons technology).
Then the rise of gunpowder and portable guns swiftly made them obsolete in the Western world. In the several hundred years since swords disappeared, a lot of their history went, too, and is only now being rediscovered.
One mystery is that some swords include engravings on the blades. There's the famous Viking swords with the engraving "+ULFBERH+T", for example, that were centuries ahead of their time. Unfortunately, no one knows who or what "Ulfberht" was, but at least it's identifiable as a name.
The British Library recently started examining a sword from the 13th century that has an engraving unlike anything else. In fact, the researchers are so stumped they turned to the Internet for help.
Julian Harrison of the British Library posted this image on Twitter:
— Julian Harrison (@julianpharrison) August 3, 2015
If you can't make it out, the inscription is "+NDXOXCHWDRGHDXORVI+".
The theories on the Internet range all over. Some people are spotting abbreviations like "CHWDN" as "churchwarden." Others are saying it's just the old-fashioned equivalent of a serial number.
Some people claim it has numerological meaning, while others link it to the Arthurian legend. However, from the crosses, it's likely something religious and Latin. Harrison thinks "ND" could be "Nostrum Dominus," or "Nomine Domini" and "XOX" could refer to the Trinity.
Unfortunately, we may never know. However, we'd love to hear any of your theories in the comments.