Roman temples consisted generally of a cella or rectangular apartment, preceded by a porch, the whole being raised on a platform, reached by stairs and enclosed by a colonnade below. Occasionally there was a double cella, with separate entrances and porches, as in that of Venus and Rome; and there are two remaining examples of circular temples—that of Vesta, on the Tiber, in Rome, and of the Sybil, at Tivoli—while still another type, that of the Pantheon of Agrippa, had a circular cella and a rectangular porch. The Corinthian order was the most frequently employed, that of the temple of Jupiter Stator being the richest, while those of the Pantheon, the Maison Carrée, at Nîmes, and of the temple of Antonine and Faustina are admirable specimens. This last is one of the best preserved temples, being very nearly entire at the present time; its frieze is of the most refined workmanship, representing allegorical animals, plants, etc. The temple of Fortuna Virilis is a good example of the Ionic order, but this order was never a favourite with the Romans. [Illustration: PLAN OF THE BATHS OF AGRIPPA CONNECTING WITH THE PANTHEON, ACCORDING TO PALLADIO. (_From Durand_)] A debased form of Ionic is that of the temple of Concord, or Vespasian, where the capital is altered to a considerable extent and a rope moulding added. A remarkable constructional feature of this temple is the relieving arch of brick, concealed behind the frieze, to diminish the weight on the lintel below. The great drum of the Pantheon, enclosed by a circular vault, is one of the earliest examples of domical architecture. A notable feature in it is the absence of the keystone, which is replaced here by an open ring, leaving an aperture for the entrance of light. The walls are pierced with niches and relieved by immense arches. The pediment of the porch is one of the most perfect remaining; in height its proportion exceeds that of Greek temples. The temple of Diana, at Nîmes, is a remarkable structure, having three aisles, the central one being decorated with niches and columns, which support an entablature and a ribbed vault. The ruined temples of Baalbek and of Jupiter Olympius, at Athens, are among the most colossal of this class of building. The Corinthian columns of the latter measure upward of sixty feet, and their capitals are of singularly fine workmanship. The Emperor Hadrian embellished Athens with numerous and splendid buildings, which to-day have assumed the colour and ruined appearance of the older constructions of the time of Pericles. Of the temple of Jupiter Olympius there are scarcely more than a dozen columns standing of the original one hundred and twenty. The Turks ground up many of them to make lime for their mortar.