Gettysburg Battlefield monuments are "one of the largest collections of outdoor sculpture in the world." Most are in the Gettysburg National Military Park while some are at military engagement sites on private land (e.g., the Gettysburg borough). In 2008, the NPS unit managed 1,320 monuments, 410 cannon, 148 historic buildings, 2½ observation towers, and of avenues, roads, and lanes (8 unpaved).[1] Most of the Gettysburg Battlefield monuments were documented as historic district contributing structures on January 23, 2004 when approved by the Keeper of the National Register.