"What is that?"
"The tunnel which they had to build in order to bring their two pieces here."
"A tunnel?"
"Well, of course! How do you expect they got here? Let's follow the rails, in the other direction, and we'll soon come to the tunnel."
As he anticipated, the two sets of rails joined a little way back and they saw the yawning entrance to a tunnel about nine feet wide and the same height. It dipped under ground, sloping very gently. The walls were of brick. No damp oozed through the walls; and the ground itself was perfectly dry.
"Èbrecourt branch-line," said Paul, laughing. "Seven miles in the shade. And that is how the stronghold of Corvigny was bagged. First, a few thousand men passed through, who killed off the little Ornequin garrison and the posts on the frontier and then went on to the town. At the same time, the two huge guns were brought up, mounted and trained upon sites located beforehand. When these had done their business, they were removed and the holes stopped up. All this didn't take two hours."
"But to achieve those two decisive hours the Kaiser worked for seventeen years, bless him!" said Bernard. "Well, let's make a start."
"Would you like my men to go with you?" suggested the lieutenant.
"No, thank you. It's better that my brother-in-law and I should go by ourselves. If we find, however, that the enemy has destroyed his tunnel, we will come back and ask for help. But it will astonish me if he has. Apart from the fact that he has taken every precaution lest the existence of the tunnel should be discovered, he is likely to have kept it intact in case he himself might want to use it again."
And so, at three o'clock in the afternoon, the two brothers-in-law started on their walk down the imperial tunnel, as Bernard called it. They were well armed, supplied with provisions and ammunition and resolved to pursue the adventure to the end.