All these arches had originally groups of statuary upon them, for which they served merely as the pedestals. Their taking the form of an arch was due to their being placed in the public way, where it was necessary to leave a passage for the street. Sometimes they were placed where two roads met, and a double arch was then made. Elaborate as the arches often were, you must keep in mind that they are only a part of the entire design, and that the least important part; the statuary, which has been destroyed by time, being really the more striking feature of the whole. [Illustration: FIG. 67.--TOMB OF CECILIA METELLA.] The tombs of Rome were very numerous, and were an important element in Roman architecture. The tomb of Cecilia Metella is of importance because it is the oldest remaining building of Imperial Rome and the finest tomb which has been preserved (Fig. 67). As you see, the tomb is a round tower. In the thirteenth century it was turned into a fortress, and so much dust has been deposited on its summit in the passing of time that bushes and ivy now grow there. Many writers describe it, and Byron in his "Childe Harold" spoke of it in some verses, of which the following is the beginning: "There is a stern round tower of other days, Firm as a fortress, with its fence of stone, Such as an army's baffled strength delays, Standing with half its battlements alone, And with two thousand years of ivy grown, The garland of eternity, where wave The green leaves over all by time o'erthrown;-- What was this tower of strength? within its cave What treasure lay so lock'd, so hid?--a woman's grave." The tomb of Hadrian, now known as the Castle of St. Angelo, is very interesting, and is one of the most prominent and familiar objects in Rome at the present day. But the tombs called Columbaria were much in use in ancient Rome, and differed essentially from those of which we have spoken, inasmuch as they were usually below the ground, and externally had no architecture. They consisted of oblong or square apartments, the sides of which were filled with small apertures of the proper size to hold an urn which contained the ashes that remained after a body had been burned, according to the Roman custom. Some of these apartments, especially when they belonged to private families, were adorned with pilasters and decorated with colors. (See Fig. 68.) [Illustration: FIG. 68.--COLUMBARIUM NEAR THE GATE OF ST. SEBASTIAN. _Rome._] The sepulchres of Rome were gradually enlarged, until, in the days of Constantine, they were frequently built like small temples above the ground, with crypts or vaults beneath them.