David Spurr of Brunswick is professor emeritus at the University of Geneva and teaches architectural history at the Midcoast Senior College. At a dinner for wealthy donors last October, Donald Trump unveiled his plans for a triumphal arch to be built on the western shore of the Potomac River, across the Arlington Memorial Bridge from the Lincoln Memorial. As a monument to celebrate the 250th anniversary of the United States, the arch would be built 250 feet high, making it by far the largest triumphal arch in the world. But the scale and placement of Trump’s proposed monument, as well...