Colross, (also historically known as Belle Air and Grasshopper Hall), is a Georgian mansion in Princeton, New Jersey; it was built as the center of an estate in the Old Town neighborhood of Alexandria, Virginia. Colross is currently the administration building of Princeton Day School. The Colross property originally occupied the entire 1100 block of Oronoco Street; Alexandria merchant John Potts developed it as a plantation and began building the mansion in 1799–1800.