"We have pine torches," said the officer.
"That will do capitally."
Paul was right. When the ladder was let down and he had descended with the lieutenant and Bernard, they saw a very large hall, whose vaults were supported by massive pillars which divided it, like a church of irregular design, into two main naves, with narrower and lower side-aisles.
But Paul at once called his companions' attention to the floor of those two naves:
"A concrete flooring, do you see? . . . And, look there, as I expected, two rails running along one of the upper galleries! . . . And here are two more rails in the other gallery! . . ."
"But what does it all mean?" exclaimed Bernard and the lieutenant.
"It means simply this," said Paul, "that we have before us what is evidently the explanation of the great mystery surrounding the capture of Corvigny and its two forts."
"How?"
"Corvigny and its two forts were demolished in a few minutes, weren't they? Where did those gunshots come from, considering that Corvigny is fifteen miles from the frontier and that not one of the enemy's guns had crossed the frontier? They came from here, from this underground fortress."
"Impossible."