As the small group of mercenaries settled down for the night, they failed to notice that some small pieces of barbed wire sticking out of the ground nearby were moving like tentacles.Until it was too late and they woke to feel it clutched around their throats and squeezing hard. As their blood spilled upon the ground the Barbed Arms had claimed yet more victims.
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.