“Unbuilt Washington,” the newest exhibition at the National Building Museum in Washington, D.C, highlights over 100 architectural projects proposed for the nation’s capital since 1791. All of the monuments, bridges, museums and other buildings were never executed—at least not according to plan. Yet, from their sketches and models rises a quirky, arguably influential cityscape that curator G. Martin Moeller calls the “the Washington that could have been.”

A close approximation of Robert Mills’ winning competition entry for the Washington Monument, for instance, is prominently figured in a lithograph (above) of the National Mall, made in 1852. The architect envisioned a 600-foot obelisk with a circular structure at its base. The pantheon would be 100 feet high and 250 feet in diameter, with 30 Doric columns, one for each state in the Union as of 1845. On top, he planned to mount a statue of George Washington in a horse-drawn carriage.

Though Mills’ design was accepted in 1845, and begun three years later, construction ground to a halt in 1856. When it resumed after the Civil War, the pantheon was scrapped, the obelisk’s dimensions height was lowered to 555 feet and its point was sharpened.