It is easy to understand how, in caves thus protected against the influence of summer heat, a great part of the ice accumulated during the winter may be preserved, and that, for an explanation of the phenomenon, it is by no means necessary to have recourse to cold blasts descending from the interior of the rock in which they are situated. It is indeed a common belief that the ice-caves are colder in summer than in winter, and consequently contain a greater abundance of ice during the former season; but this belief may well be considered as one of those popular fallacies, which—though, by dint of repetition, they come to be common articles of faith—have in fact no substantial proofs to support them. CHAPTER XVIII. ROCK TOMBS AND CATACOMBS. Biban-el-Moluk, the Royal Tombs of Thebes—The Roman Catacombs—Their Extent—Their Mode of Excavation—Touching Sepulchral Inscriptions— Antony Bosio, the Columbus of the Catacombs—The Cavaliere di Rossi—The Catacombs of Naples and Syracuse—The Catacombs of Paris. The remoteness of caves and grottoes from the busy haunts of life, their eternal silence and their nightly gloom, have ever pointed them out as fit resting-places for the dead. From the earliest times they have been used as sepulchral vaults, and where nature neglected to hollow out the rock, it has often been excavated for this purpose by the hand of man. Thus the Pharaohs of Egypt rested not in temples and mausoleums reared in the heart of cities, but they chose the desert-ravine for their sepulchre, and hid their tombs in deep excavations in the earth. A more impressive scene can hardly be imagined than that which is afforded by these splendid memorials. Of all such monuments which still mark the site of ancient Thebes, perhaps none are more striking to the traveller than the royal tombs—Biban-el-Moluk—which the pride of monarchs, whose very name is now a mystery, excavated four thousand years ago in the bosom of the Libyan mountains.