The exterior (Fig. 56) was less successful than the interior. The gabled porch of twelve superb granite columns 50 feet high, three-aisled in plan after the Etruscan mode, and covered originally by a ceiling of bronze, was a rebuilding with the materials and on the plan of the original pronaos of the Pantheon of Agrippa. The circular wall behind it is faced with fine brickwork, and displays, like the dome, many curious arrangements of discharging arches, reminiscences of traditional constructive precautions here wholly useless and fictitious because only skin-deep. A revetment of marble below and plaster above once concealed this brick facing. The portico, in spite of its too steep gable (once filled with a “gigantomachia” in gilt bronze) and its somewhat awkward association with a round building, is nevertheless a noble work, its capitals in Pentelic marble ranking among the finest known examples of the Roman Corinthian. Taken as a whole, the Pantheon is one of the great masterpieces of the world’s architecture. [Illustration: FIG. 57.--FORUM AND BASILICA OF TRAJAN.] +FORA AND BASILICAS.+ The fora were the places for general public assemblage. The chief of those in Rome, the +Forum Magnum+, or +Forum Romanum+, was at first merely an irregular vacant space, about and in which, as the focus of the civic life, temples, halls, colonnades, and statues gradually accumulated. These chance aggregations the systematic Roman mind reduced in time to orderly and monumental form; successive emperors extended them and added new fora at enormous cost and with great splendor of architecture. Those of Julius, Augustus, Vespasian, and Nerva (or Domitian), adjoining the Roman Forum, were magnificent enclosures surrounded by high walls and single or double colonnades. Each contained a temple or basilica, besides gateways, memorial columns or arches, and countless statues. The +Forum of Trajan+ surpassed all the rest; it covered an area of thirty-five thousand square yards, and included, besides the main area, entered through a triumphal arch, the Basilica Ulpia, the temple of Trajan, and his colossal Doric column of Victory. Both in size and beauty it ranked as the chief architectural glory of the city (Fig. 57). The six fora together contained thirteen temples, three basilicas, eight triumphal arches, a mile of porticos, and a number of other public edifices.[14] Besides these, a net-work of colonnades covered large tracts of the city, affording sheltered communication in every direction, and here and there expanding into squares or gardens surrounded by peristyles. [Footnote 14: Lanciani: _Ancient Rome in the Light of Recent Discoveries_, p. 89.] [Illustration: FIG. 58.--BASILICA OF CONSTANTINE. PLAN.]