The Groton Battle Monument is an obelisk granite monument that was dedicated in 1830 to the men who had defended Fort Griswold during the massacre by Benedict Arnold's troops of Colonial militia and locals. During the centennial year, 1881, the top was enclosed and the monument was increased to a height of 134 feet. Memorial Day-Labor Day: Open Daily, 9am-5pm. Labor Day-Columbus Day: Open weekends.