The present extent of the Catacombs is the result, not of primary intention, but of the contact of separate areas of comparatively limited original size, and the inosculation, as it were, of their distinct galleries. This is apparent from the fact that this contact and junction sometimes take place between areas of different levels, causing a break in their horizontal continuity, like the “faults” or dislocations common in geological strata. Sometimes, too, this junction between two adjacent areas takes place through a tier of graves, and evidently formed no part of the original design. These separate areas were originally, as we shall see in the following chapter, private burial places in the vineyards of wealthy Christian converts, and were early made available for the interment of the 38 poorer members of the infant Church. In accordance with a common Roman usage the ground thus set apart for the purpose of sepulture was placed under the protection of the law, and was accurately defined, to secure it from trespass or violation. While the protection of the law was enjoyed, the excavations were strictly confined within the limits of these areas, and lower _piani_ were dug rather than transgress the boundary. But when that protection was withdrawn the galleries were horizontally extended, often for the purpose of facilitating escape, and connections were made with adjacent areas, till the whole became an intricate labyrinth of passages and chambers. These areas are still further distinguished by certain peculiarities in the inscriptions, _cubicula_, and paintings, and were greatly modified by subsequent constructions. It has till recently been thought that the Catacombs were originally excavations made by the Romans for the extraction of sand and other building material, and afterward adopted by the Christians as places of refuge, and eventually of sepulture and worship. This opinion was founded on a few misunderstood classical allusions and statements in ancient ecclesiastial writers, and on a misinterpretation of certain accidental features of the Catacombs themselves. It was held, nevertheless, by such eminent authorities as Baronius, Severano, Aringhi, Bottari, D’Agincourt, and Raoul-Rochette. Padre Marchi first rejected this theory of construction, and the brothers De Rossi have completely refuted it. An examination of the material in which these sand pits and stone quarries and the Catacombs were respectively excavated, as well as of their structural differences, will show their entirely distinct character.