Read The Bridge
 
“H-How big was the crystal mound?”
 
Xenilla only shrugged, forming another crystalline casing around the aerenth fragment.  
“About as tall and wide as myself. I destroyed the rest of it after taking the sample I brought you.”
 
Now it was Key Ring’s turn to try and compete with Blade Dancer on who’s face could go paler. He gave her a run for her money as his eyes shot open.  
“By Bonnie’s pen…”
 
“Let me guess… size indicates something?”
 
“S-Size scales with power… If you are telling the truth, whoever made an aerenth crystal that big had enormous magical potential.”
 
“And allow me to guess…”  
Xenilla applied more layers of his own crystal to cloak the aerenth, not wanting to take any chances.  
“To fuel that potential in dark magic in the creation of large aerenths, they had to have been experiencing large amounts of malefic thoughts or emotions at the time.”
 
“Enough greed to pillage, enough hate to murder.”
 
Blade Dancer had managed to get a hold of one of Key Ring’s history books, flipping through some of the pages about dark magic use. She was quickly becoming glad the most magic she ever used was shoving a cloud or two.  
“Who all could do something like this in the past? What sort of ball park are we talking about with our suspect?”
 
Key Ring chewed on his lip, pulling up some slides he’d been using for his class. The young stallion whipped out the pair he’d been looking for and flipped on the projecter. The photograph of a dark alicorn with ebony fur and a starry mane illuminated one half of the white board, the illustration of a malefic looking unicorn in steel armor covering the other half of the board.  
“Well if we are talking just straight up dark magic usage, the most powerful and notable would be the scourge of the Everfree, Nightmare Moon. In terms of crystal magic use, that would be the former ruler of the empire, King Sombra.”
 
Xenilla studied the two images, the ancient illustration in particular. Something about the way the eyes were drawn in seemed vaguely familiar. However it was something Key Ring said that got his attention first.  
“Wait… ‘King’ Sombra?”
 
“Um, yes?”
 
“He was a king, and yet ruled over, an empire?”
 
“I… don’t see how that’s important right now…”
 
Clad across Xenilla’s face was the most blank, annoyed face one could possibly imagine. His neck and expression drooped somewhat, dumbstruck.  
Then why wasn’t he an emperor-…. oh Good Tanaka the male rulers are just as stupid..  
Xenilla grumbled, shaking his head to try and clear away his annoyance.  
“Never mind, move on. What can you tell me about them.”
 
“Well, thankfully if you are suspecting what I think you are suspecting, don’t. Both of them are out of the picture. Nightmare Moon was purified and Sombra was killed not long ago.”
 
“Oh? Who or what killed Sombra?”
 
“The crystal heart so I’m told, by Spike Sparkle and Princess Cadenza.”
 
Something in Xenilla’s mind snapped to attention, making him quickly turn to face Key Ring. The gears in his head were turning. Something about the placement of the aerenth in the market place was beginning to make sense.  
“Wait… It was Empress Cadenza who killed Sombra?”
 
“Through her rallying the nation into fueling the crystal heart, yes.”
 
Xenilla turned and studied the ancient illustration. His eyes were beginning to narrow, as if staring down an opponent. Something told him he wasn’t far off.  
“And this, Sombra. He ruled over the empire prior to the Empress, correct?.”
 
“Indeed, though they might not tell you much of that unless you dug for information. King Sombra ushered in the darkest age in imperial history. Almost all living crystal ponies lived during his rule and have a taboo about speaking of him.”
 
Hm… only lead to go on. If Terra’s wars taught me anything, it’s never assume an opponent is dead..