The Philadelphia Merchants' Exchange Building, designed by William Strickland and constructed by John Struthers in 1834, was built to accommodate commercial transactions for the city's growing mercantile industry. Serving as the Philadelphia Stock Exchange at the turn of the century, the building was converted to a produce market in 1922 with the addition of an awning and vendor stalls. Incorporated into Independence National Historical Park and restored in the early 1950's, the Merchants' Exchange was designated a National Historic Landmark in 2001 and currently houses NPS administrative offices. Constructed primarily of Pennsylvania Blue Marble, the building is notable for its monumental and innovative design in the Greek Revival style.