An extremely shiny piece of bling, so big and amazing that it inspires anyone who sees it to ask questions about its origins, the bearer, and most anything else they can think of.
A classical enchanted weapon…
A rumour of the knights of some powerful king that sleep until danger threatens the kingdom.
The truth is that they were rebels, trying to split the kingdom. Once captured they were put into an enchanted sleep, protected from age and harm, until their aims have been carried out by others in which case they will awaken.
There is a loophole in the spell in that trying to take one of their weapons will also awaken them.