Francis had first attempted to discourage their nightly digging by increasing the thickness of the brush pile over his trench, and by surrounding it with a ring of stones set tightly in a furrow. But on the previous night, something had leaped to the top of his brush pile and howled while Francis lay shivering below, whereupon he had determined to fortify the burrow, and, using the first ring of stones as a foundation, had begun to build a wall. The wall tilted inward as it grew; but since the enclosure was roughly an oval in shape, the stones in each new layer crowded against adjacent stones to prevent an inward collapse. Brother Francis now hoped that by a careful selection of rocks and a certain amount of juggling, dirt-tamping, and pebble-wedging, he would be able to complete a dome. And, a single span of unbuttressed arch, somehow defying gravity, stood there over the burrow as a token of this ambition. Brother Francis yelped like a puppy when the pilgrim rapped curiously at this arch with his staff.