At the beginning of the present century, tokens of a reviving interest in them may be traced in the proceedings of the Roman Archæological Society. But it was not until the year 1840 that this interest spread to any wide circle. The main impulse to it was then given by Father Marchi, S.J., who had been appointed _custode_ of the Catacombs, and devoted himself to their study. In 1841 he began to publish a work on the monuments of early Christian art. Only the first volume, however—on architecture—was ever published, and then it was abandoned, partly in consequence of the political troubles of the times, by which his own Order was so seriously affected, but chiefly because, through the new discoveries that were made, he became conscious of its grave imperfections. He saw that he had begun to publish prematurely. He had, however, imparted his own enthusiasm to one of his scholars, who was at first the frequent companion of his subterranean exploring expeditions, whom he soon recognised as a valuable fellow-labourer, and whom he finally urged in the most pressing manner to undertake the work which he found too great for his own failing strength. This scholar was Giovanni Battista de Rossi, a Roman gentleman of good family, who has now for more than thirty years devoted his means, time, and talents to the prosecution of the task intrusted to him. It has been well said that “archæology, as tempered and directed by the philosophic spirit, and quickened with the life and energy of the nineteenth century, is a very different pursuit from the archæology of our forefathers, and has as little relation to their antiquarianism as modern chemistry and modern astronomy have to their former prototypes, alchemy and astrology;” and nowhere can the justice of this remark be more keenly appreciated than in comparing De Rossi’s works on the Catacombs with all that have gone before them. It is true that he has had some advantages which his predecessors had not; he has had access to newly recovered, or more carefully edited, documents, amongst which are even ancient guides to those sanctuaries, or at least exact descriptions of them, before they had been abandoned and their sacred treasures removed. He has also had the assistance, as intelligent as it has been indefatigable, of a brother whose mechanical genius has invented an instrument whereby the process of surveying and mapping any subterranean excavations has been rendered infinitely more easy, as well as more accurate, than it was before. But, after all, the chief secret of De Rossi’s wonderful success is to be sought for rather in his own patient industry, his scrupulous caution, and the excellence of his scientific method, than in any extraordinary superiority of his literary or physical apparatus. He has studied every monument in its own place. He has examined with his own eyes every detail of the subterranean topography where it has been possible to penetrate, and then recorded his