When you think of a classic American college campus, you probably envision a set of pastoral images: a demure brick rowhouse crowned with a white steeple, a gargoyle perched on a limestone archway, a domed library on a sunlit grass quadrangle. Often far from cities or shielded from them by gates and walls, campuses exude a sense of refuge. Thomas Jefferson famously wanted the University of Virginia to resemble a kind of ‘‘academical village.’’