The first boardwalk was built in 1870 along a portion of the beach in an effort to help hotel owners keep sand out of their lobbies. Businesses were restricted and the boardwalk was removed each year at the end of the peak season. Because of its effectiveness and popularity, the boardwalk was expanded in length and width, and modified several times in subsequent years. The historic length of the boardwalk, before the destructive 1944 Great Atlantic Hurricane, was about 7 miles (11 km) and it extended from Atlantic City to Longport, through Ventnor and Margate.

Answer this question, if possible (if impossible, reply "unanswerable"): In what year was the first boardwalk built in Atlantic City?
1870