On the episode "The Witch's Quickening", Morgana stole for Mordred a crystal called "The Crystal of Neahtid", a magical object that was really powerful but one that only few could use. Many priestesses died trying to protect this crystal and its power was beyond control for most sorcerers. It was said that, if not returned to Camelot, it would give to Alvarr's men such strength that they would have easily destroyed the kingdom. However, before Mordred had the chance to master its use, Arthur and his men came to the rescue and returned the crystal to Camelot's vaults.
Most of this is known to most people around the wiki, I know. The thing is, back then at series 2 Kilgharrah found hillarious that Morgana wanted to use the crystal, probably thinking that she was not good with her magic. However, when she conquered Camelot in series 3, she definitely was around Mordred's level of series 2. Even if she wasn't, Morgause definitely was. So, why did they not use that thing in order to make their forces even more powerful? If it had such power, they would have conquered not only Camelot, but all five kingdoms with relative ease. Also, thinking that priestesses died trying to protect it from Uther, it makes someone wonder how Morgause didn't seek to get her hands on it. What's even moe mysterious is that not even Morgana on series 4, whose magic had outstandingly grown to the point of rivaling Merlin's, did not try to use the crystal. I mean, she had stolen it for someone else in the past, knowing its strength, and now that she can control it, and nobody's there to stop her from stealing it, she does not seek it? In my opinion, the only reason for that is that the writers must have completely forgotten its existence!
Now, I think that it would be a nice plotline for the first or last few episodes to have Morgana sneak into Camelot and steal that crystal. Her magic power would increase tenfold and Merlin would have to hurry and get it back before she did something evil like killing Arthur, destroying Camelot e.t.c. She could also find another use for it, like commanding dragons (much to Kilgharrah's disatisfaction) resurrect old dead people, learn who Emrys is or who knows what else! What do you guys think?