Michelangelo Pistoletto’s work has undergone a number of profound transformations over the last 55 years, none more dramatic than those that occurred during a few incendiary years in the mid-1960s. Works from this period provide the core of “Michelangelo Pistoletto: From One to Many, 1956–1974,” which debuted at the Philadelphia Museum of Art and is now on view at Rome’s MAXXI (through August 15). The show traces Pistoletto’s moves from painting to three-dimensional work, to collaborative performances and installations. Along the way, he made some of his best-known works, including Venus of the Rags (1967), which joins a reproduction of a classical nude and a pile of multi-colored clothes. An icon of the Arte Povera movement in Italy, Pistoletto’s Venus has also become emblematic of late-1960s sculpture in general.