From the cupola of St. Peter’s, the most favourable station for a panoramic view of all the monuments and buildings of the Eternal City, the eye is also best able to embrace at one glance the general topography of the catacombs or of subterranean Rome. Fifteen great consular roads, over which the victorious legions once marched out to subjugate the world, radiate from the centre of the town, and furrow the arid Campagna, until they are finally lost in the hazy distance. To the right and left of these causeways the catacombs have been hollowed out in the depths of the earth, and, though separated by the Tiber into two distinct regions, yet their various subdivisions trace a vast circle, the size of which may be measured by the circumference of the town itself. To form some idea of their extent, we must fancy an intricate wilderness of galleries and arched alcoves with their layers of sarcophagi, one above another; their _lucernaria_, for light or ventilation; their stairs, straight or winding; and all this, not on one level only, but floor beneath floor—one, two, three, four, five—hewn out on a labyrinthine, yet harmonious and economic plan. Network is perhaps a feeble description of these vast and intricate mazes; a spider’s web seen through the glass of a naturalist, or rather four or five spiders’ webs, one within the other, would seem a more fitting illustration. Such is the immensity of this city of the dead that, according to the opinion of those who have made themselves best acquainted with all its subdivisions, their galleries, supposing them ranged in a line, would form a street 900 miles long, and lined by no less than six millions of tombs!