Louisville, the largest city in the Commonwealth of Kentucky and the 30th-most populous city in the United States, is one of two cities in Kentucky designated as first-class. Louisville is the historical seat and, since 2003, the nominal seat of Jefferson County. It was founded in 1778 by George Rogers Clark and is named after King Louis XVI of France, making Louisville one of the oldest cities west of the Appalachian Mountains. Sited beside the Falls of the Ohio, the only major obstruction to river traffic between the upper Ohio River and the Gulf of Mexico, the settlement first grew as a portage site. An important internal shipping port in the 19th century, Louisville is today most well known for the Kentucky Derby, the widely watched first race of the Triple Crown of Thoroughbred Racing.