January 1st, 1776. Where? Located at Prospect Hill Avenue and Munroe Street, Prospect Hill Castle is important to Somerville's, Massachusetts history. On January 1, 1776, General George Washington ordered that a new flag be raised on a 76-foot schooner mast placed on Prospect Hill. Representing the 13 united colonies during the Revolutionary War, this was the first true "American" flag flown in [what is now] the United States. The tower that now stands atop Prospect Hill was erected in 1902, and remains one of Somerville's oldest and greatest landmarks. Every year on January 1, the historic flag raising is recreated at the Prospect Hill Tower, commemorating the great historical value of one Someville's most treasured locations.