M. de Montriveau’s companions were alone on board the vessel, and out of sight of every human eye. No one from the deck of a passing vessel could have discovered either the brig hidden among the reefs, or the men at work among the rocks; they lay below the ordinary range of the most powerful telescope. Eleven days were spent in preparation, before the Thirteen, with all their infernal power, could reach the foot of the cliffs. The body of the rock rose up straight from the sea to a height of thirty fathoms. Any attempt to climb the sheer wall of granite seemed impossible; a mouse might as well try to creep up the slippery sides of a plain china vase. Still there was a cleft, a straight line of fissure so fortunately placed that large blocks of wood could be wedged firmly into it at a distance of about a foot apart. Into these blocks the daring workers drove iron cramps, specially made for the purpose, with a broad iron bracket at the outer end, through which a hole had been drilled. Each bracket carried a light deal board which corresponded with a notch made in a pole that reached to the top of the cliffs, and was firmly planted in the beach at their feet. With ingenuity worthy of these men who found nothing impossible, one of their number, a skilled mathematician, had calculated the angle from which the steps must start; so that from the middle they rose gradually, like the sticks of a fan, to the top of the cliff, and descended in the same fashion to its base. That miraculously light, yet perfectly firm, staircase cost them twenty-two days of toil. A little tinder and the surf of the sea would destroy all trace of it forever in a single night. A betrayal of the secret was impossible; and all search for the violators of the convent was doomed to failure. At the top of the rock there was a platform with sheer precipice on all sides. The Thirteen, reconnoitring the ground with their glasses from the masthead, made certain that though the ascent was steep and rough, there would be no difficulty in gaining the convent garden, where the trees were thick enough for a hiding-place. After such great efforts they would not risk the success of their enterprise, and were compelled to wait till the moon passed out of her last quarter.