To this question their very form seems to supply the only possible answer. They were made to bury the dead. This is undeniably the first and principal use to which they were put. It is no less certain that this was also the object for which they were designed. Time was, indeed, when learned men shrank from this conclusion, and suggested, that though unquestionably they were used as burial-places, yet perhaps this was only an afterthought, and that they may have been originally designed for something else. The building of Rome, it was said, must have required vast quantities of stone and of sand to make cement; perhaps, therefore, in the Roman Catacombs we have only lit upon a certain number of exhausted, or rather deserted, sandpits and quarries, which later generations availed themselves of, for economy’s sake, as places of burial. [Illustration: _Plan of Arenaria at St. Agnes’._] This theory sounds very plausible at a distance from the places themselves; but on closer examination on the spot there are found fatal objections to it. One is, that they happen not to be excavated either in sand or in stone, but precisely in a rock of intermediate consistency, too solid to be used as sand, too soft and friable to be used as building-stone; and perhaps this might be allowed to stand as a peremptory refutation of the theory in question. But we will add another argument, not less simple or less conclusive, drawn from the different forms of the two kinds of excavation. Compare the subjoined plan with that which has been give before on page 5. These two excavations occur in the same place. They overlie one another on the Via Nomentana, and they are here drawn on precisely the same scale. Could they be mistaken one for the other? Do they look like parts of the same plan? One represents the long, narrow, straight streets or galleries and occasional chambers of a catacomb; the other, the broad, tortuous, and irregular excavations of a sandpit. The makers of both had each a definite object in their work, but these objects were distinct from, and even opposed to, one another; and hence the two systems have distinct, and even contrary, characteristics. The only point in common between them is, that both were carried on underground, and both wished to disturb as little as possible the superficial soil. But the quarryman aimed at taking out as much of the material as he could, and with the least trouble; whilst the Christian _fossor_ desired to extract as little of the material as was consistent with his object of providing hundreds or thousands of graves. Hence we find in the sandpit broad roads, admitting the use of horses or carts, and these roads well rounded off at the corners for the facility of passing to and fro; whereas the paths of the cemetery cross one another at right angles, that so every part of their walls may be available for purposes of sepulture, whilst they are so narrow that two men can scarcely walk abreast in them.