The Presidio served as a military post under the flags of Spain (1776-1822), Mexico (1822-48), and the United States (1848-1994). As a U.S. Army post, the Presidio protected commerce and trade, and played a logistical role in every major U.S. military conflict from 1848 until closure. Within its boundaries are more than 500 historic buildings, a collection of coastal defense fortifications, a national cemetery, an historic airfield, a saltwater marsh, forests, beaches, native plant habitats, coastal bluffs, miles of hiking and biking, and some of the most spectacular vistas in the world. Leashed pets are permitted in the park, but are not allowed in the buildings. Leashes must be no longer than six feet.