Cities as art centers have not always had the attention they deserve, especially in art exhibitions, because of the daunting problems of scale as well as the problems of representation of both the architectural environment and the unmovable monuments. There have been some truly notable exceptions, with particular relevance to this ambitious effort on Rome: Philadelphia’s own Second Empire Paris exhibition as well as Detroit’s 18th-Century Naples (1981). Once more Philadelphia has taken on a formidable “millennium show” challenge, and has done it justice. This exhibition is a revelation as well as a revision. The Splendor of 18th-Century Rome is a revision, because art history’s attention has been focused until now principally on the Ancien Regime and the Rococo and Neoclassical phases of Paris in that century. The classic studies of baroque art in Italy by Haskell and Wittkower stop short of this period, where they attend chiefly to other cities. So this exhibition also offers a revelation, because it also makes patent how much central artistic invention either happened in Rome (which was, after all, one of the principal destinations of the Grand Tour for visitors of all kinds, certainly for artists) or else drew upon Rome’s traditions (antique,...