Klimian spread a map of Paris on the ground.
"This is Père Lachaise Cemetery." Klimian pointed his wand at the map, and a point of light immediately appeared on it. "This is the Paris Catacombs."
"So?" Severus asked, looking at the map.
"Do you remember what Mr. Grey told us earlier? The point in front of The Hunchback of Notre-Dame is France's center. I remember old maps being drawn according to how many days' journey a place was from Paris. Whether Lyon in the south or Caen in the west, they all lay on the same concentric circle." Klimian waved his wand, and a small ring of light appeared around Père Lachaise Cemetery. "This is the circle my teacher and the Scamander brothers set up seventy years ago."
Then he waved his wand again. The circle's diameter expanded considerably, and its tangent point was precisely the Paris Catacombs. "If the origin point at The Hunchback of Notre-Dame was set for the living aboveground, then Père Lachaise Cemetery was set for the dead and the spirits. If my teacher had failed back then, the fire Grindelwald summoned would not only have destroyed Paris, but might also have disturbed the spirits beneath the ground."
"I remember Dumbledore inviting the Skeleton Song-and-Dance Troupe one Halloween," Severus said. "Those bones laid underground could become a skeleton army."
"Why would you think that?"
"Because Albus Dumbledore and Gellert Grindelwald had a very special relationship." Severus gave a false smile. "They were closer than blood brothers."
"They were both searching for the Deathly Hallows," Klimian said. "They say the Resurrection Stone can summon an army of Inferi."
Severus said nothing. He drew his wand as well.
"Grindelwald wasn't just trying to destroy Paris. He wanted to build an army of skeletons and Inferi." Klimian spoke furiously.