Other definite areas of this Catacomb have been recognized and their outlines defined. Indeed, Father Marchi asserts that this is “the colossal region of _Roma Sotterranea_, all the rest being only small or middling provinces.”[311] About a hundred yards from the “Papal Crypt” is the tomb of another celebrated martyr and bishop, St. Eusebius; the _graffiti_ on the walls, the stairway, and the decorations of which attest the reverence in which it was held. While digging here in 1856, De Rossi found the important epitaph of Eusebius before given.[312] Intimately connected with this are also the adjacent cemeteries of St. Soteris, a virgin martyr of the same family from which Ambrose was descended; and that of St. Balbina, of vast extent, in several _piani_, and on a scale of unusual grandeur. These are as yet only partially explored, and promise the richest results to future examination. That of St. Balbina has many double, and even quadruple, _cubicula_, and the largest and most regular group of subterranean chambers that have yet been discovered, all lighted by one large hexagonal shaft. They were evidently excavated for worship, not for sepulture. This Catacomb was enlarged and beautified by Mark, bishop of Rome, in A. D. 330, who was buried in a basilica erected over these tombs. These several areas were at first all distinct properties, and as carefully restricted within their respective limits as would be 183 buildings above ground. When, however, the sepulchres of the Christians, no longer protected by law, were invaded by the persecutors, the different areas were connected by a vast and bewildering labyrinth of cross passages for the purpose of facilitating escape and of furnishing additional space for interment. As the areas, even when contiguous, were often at different levels, a good deal of ingenuity was exercised by the fossors in effecting a junction of the different galleries; though often they had to break through _loculi_ and _cubicula_ for that purpose. Thus the area we have described so fully is five feet lower than that which is adjacent on one side, which enables us to determine its exact limit. We will now take a more rapid survey of the other principal Catacombs of Rome.