German-born art historian Richard Krautheimer from New York University, visiting scholar at Vassar, lectured on "The Piazza of St. Peter's."   Professor Krautheimer, an émigré during the Nazi rise to power, taught at Vassar from 1937 before becoming the Jayne Wrightsman Professor of Fine Arts at NYU in 1952.  His Studies in Early Christian, Medieval and Renaissance Art appeared in 1969.