Knights of Medhir

Over three hundred years ago this group of seven knights were seduced by a sorceress's call. One by one they succumbed to her power, becoming a terrifying and brutal force that rode through the lands leaving death and destruction in their wake. They were only stopped when the sorceress herself was killed, as without her power to animate them, they became lifeless. It is said they can wake again if a strong enough power summons them. While summoned, no weapon can harm or kill the Knights; only if the spell animating them is broken can they be stopped.

The spell used by Morgause to chant the knights alive was: "Cnihtas Medhires, éower sáwla sind min sáwla. Onwác and cóm hér eft. Rid eft ond forsliehð eft. Gehðu, Uther Pendragon", while the one she used to stop them was "Astýre ús þanonweard! Cnihtas Medhires, éower sáwla. Rid eft ond forsliehð eft.".

Trivia

 * They are comparable to the Ringwraiths in Lord of the Rings by JRR Tolkein.