These results are chiefly due to the labors of two Romans, one a priest and the other a layman, the Padre Marchi, and the Cavaliere de Rossi, who have devoted themselves with the utmost zeal and with great ability to the task of exploration.  The present Pope, stimulated by the efforts of these scholars, established some years since a Commission of Sacred Archeology for the express purpose of forwarding the investigations in the catacombs; and the French government, soon after its military occupation of Rome, likewise established a commission for the purpose of conducting independent investigations in the same field.[A]

[Footnote A:  In 1844, Padre Marchi published a series of numbers, seventeen in all, of a work entitled Monumenti delle Arti Cristiane Primitive nella Metropol del Cristianesmo.  The numbers are in quarto, and illustrated by many carefully executed plates.  The work was never completed; but it contains a vast amount of important information, chiefly the result of Padre Marchi’s own inquiries.  The Cavaliere de Rossi, still a young man, one of the most learned and accomplished scholars of Italy, is engaged at present in editing all the Christian inscriptions of the first six centuries.  No part of this work has yet appeared.  He is the highest living authority on any question regarding the catacombs.  The work of the French Commission has been published at Paris in the most magnificent style, in six imperial folio volumes, under the title, Catacombes de Rome, etc., etc. Par Louis Perret. Ouvrage publie par Ordre et aux Frais du Gouvernement, sous la Direction d’une Commission composee de mm.  Ampere, ingres, MERIMEE, VITET.  It consists of four volumes of elaborate colored plates of architecture, mural paintings, and all works of art found in the catacombs, with one volume of inscriptions, reduced in fac-simile from the originals, and one volume of text.  The work is of especial value as regards the first period of Christian Art.  Its chief defect is the want of entire accuracy, in some instances, in its representations of the mural paintings,—­some outlines effaced in the original being filled out in the copy, and some colors rendered too brightly.  But notwithstanding this defect, it is of first importance in illustrating the hitherto very obscure history and character of early Christian Art.]

The Roman catacombs consist for the most part of a subterranean labyrinth of passages, cut through the soft volcanic rock of the Campagna, so narrow as rarely to admit of two persons walking abreast easily, but here and there on either side opening into chambers of varying size and form.  The walls of the passages, through their whole extent, are lined with narrow excavations, one above another, large enough to admit of a body being placed in each; and where they remain in their original condition, these excavations are closed in front by tiles, or by a slab of marble cemented to the rock, and in most cases bearing an inscription.  Nor is the labyrinth composed of passages upon a single level only; frequently there are several stories, connected with each other by sloping ways.