Since ancient times societies have employed outposts to secure new frontiers. The Presidio of San Francisco, founded in 1776, offers a classic case study of this phenomenon. Under the flags of Spain, Mexico, and the United States, this bastion by the bay stood guard over a major port that evolved into the storied city by the Golden Gate. During the early phases of the presidio's precarious existence, the Spanish erected a less-than-imposing fort and a pair of tiny artillery emplacements armed with antiquated cannons. In the early 1820s, the Mexican government inherited the burden of the bay's defense and the upper reaches of Alta California. Their efforts proved inadequate to stave off the onslaught of the United States as it marched westward in quest of manifest destiny. By the 1840s the US Army constructed major defense bulwarks on both sides of the "harbor of harbors." Early earthen and brick bastions gave way to steel and concrete, and eventually missiles bearing nuclear warheads studded the landscape. These previously formidable sentinels now stand silent and empty. Former military reservations no longer poise ready for war. Nearly two and a half centuries after the first band of King Carlos III's lancers planted the Spanish banner on windswept dunes, this once remote military outpost now serves a new purpose as a magnificent national park. Swords have been beaten into proverbial plowshares, but at a cost of sweat and blood by generations of troops, their families, and others, beginning with the peninsula's original inhabitants to later stalwart soldiers from three nations. Some of them achieved fame, but most led ordinary lives. Both this unique place and the many people who made their homes here form an integral part of our nation's fascinating, complex past.