In ancient Rome, social appearance and respectability were everything. The most hated men were punished with damnatio memoriae, damnation of memory. Every trace that a person had ever lived was removed. Busts were shattered, freizes were marred, records were struck. Any sign of the hated figure was destroyed.
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.