Society Hill contains the largest concentration of 18th century and early 19th century buildings in the United States. It is also has historical significance as the first urban renewal era project based on preservation. The Post-World War II development of the neighborhood under the Urban Renewal Program included not only the rehabilitation of historic structures, but also the integration into the neighborhood fabric of new construction town houses, a limited number of strategically placed high-rise buildings, neighborhood serving retail, historic churches, expanded neighborhood schools, and landscaped open spaces.