"Anyone who attacks Golgotha will attack from above—to gain horizontal access, the distance is too great. This means they will have to tunnel downwards, either through fresh rock or through the column of rubble with which this ventilation shaft will be filled. In either case, they will discover, when they are about halfway down, a stratum of sand, three to five meters in depth, spread across the whole area. I need hardly remind you that, in nature, pockets of sand are never found in the middle of igneous rock!"