Public hospitals trace their history back to public almshouses in 16th century England. The earliest public almshouse in the United States evolving into a hospital became known as Philadelphia General Hospital, opening about 1731 and formally closing in 1977. In the mid-1980's more than 7,500 hospitals existed in the United States, of which most were general medical and surgical-care facilities. Half of that total had more than 100 beds. Hospitals may be classified by the type of services offered. General hospitals are equipped to treat a variety of common diseases and injuries. Special hospitals treat specific diseases and special groups of patients.