The most famous circular example, as well as the most impressive of Roman temples to the modern mind, is the =Pantheon=. Investigation has proved that the circular part or Rotunda occupies the site of an earlier nymphæum, on the south side of which, in the reign of Augustus, <small>B.C.</small> 27, Agrippa erected a temple, consecrated to the Divinities of the Julian house under the name of Pantheum (“all-holy”). Hence the inscription on the frieze of the present portico: “M. Agrippa L. F. Cos. tertium fecit.” This temple, which, from Pliny’s account seems to have had a dome, was destroyed in the great fire in <small>A.D.</small> 80. The present edifice was built by Hadrian, <small>A.D.</small> 120-124. The Rotunda occupies, as we have said, the site of an ancient nymphæum, the floor of which, however, was raised 8 feet. Agrippa’s portico was removed from the south to the north side and set up with a front of 8 columns instead of 10. There are 16 in all. The portico is supported by 16 Corinthian columns, each a granite monolith 42½ feet high, with marble Corinthian capitals. The tympanum was originally filled with bronze reliefs, representing a _gigantomachia_, or battle of the gods and giants. The walls of the rotunda, which are of solid tufa concrete, faced with thin bricks, are nearly twenty feet thick. This mass was partly to support the dome and partly to admit of eight recesses, opening from the interior. One forms the entrance, while three of the others are semicircular in plan and the remaining four rectangular. The exterior walls, carried far above the spring of the dome, was veneered with porphyry and marble and enriched with Corinthian pilasters and sculptured ornament, a considerable part of which still exists.