After the war, he adopted engineering as a profession. In 1801, Williams was a major, Corps Artillerists engineer, and Inspector of Fortifications. In 1802, President Thomas Jefferson appointed him commander of the newly created Corps of Engineers and the U.S. Military Academy at West Point. Thus, he was the first Chief Engineer and First Superintendent of West Point of the reestablished Corps. Through his work as Chief Engineer, there is a clue as to who designed the Corps insignia. Between 1807 and 1812, he designed and constructed Castle Williams to defend New York Harbor. The gateway to that castle-style fortification bore an eagle over the center. Other examples included Castle Pinckney in Charleston, South Carolina and Castle Clinton, which also defended New York Harbor. An assistant on his staff was Colonel Alexander Macomb, who became the Chief Engineer, 1 June 1821 through 24 May 1828. In 1828, he was elevated to Commanding General of the U.S. Army. In 1807, he made the earliest known drawing of the Engineer Button adorned with a castle motif, worn on the uniforms of the West Point cadets during the War of 1812. Another engineer officer—Colonel Richard Delafield, superintendent of the military academy—added the turreted castle to the new uniform for the West Point cadets in 1838. Macomb—as Commanding General of the U.S. Army—had an active part in the design of the new uniform. The castle was also a major element in the architectural design of the buildings at West Point, as typified by the old library built in 1841 that survived until 1961, when it was torn down. Delafield supervised the design and construction of the buildings destroyed by the fire, including the old library. From the evidence, one would conclude that Williams and Macomb, both familiar with French military tradition and heraldry, designed not only the Corps castle emblem but also the Essayons button. Although Macomb's design appeared in 1807, the authoritative description of the button appeared in February 1840, in General Orders 7, AGO: 'Essayons,’ a bastion with embrasures in the distance, surrounded by water, and the rising sun, the figures to be of dead gold upon a bright field". While the designs of the emblem and the button have changed, the castle remains a distinctive symbol of the U.S. Army Corps of Engineers. Captain Alden Partridge, Acting Superintendent of the United States Military Academy from 1808–1817, was described by General George