Since 1718, when the armed Presidio de Béxar was established to defend the Spanish missions, the military has played a key role in San Antonio’s development, and it remains one of the largest employers in town today. The 3,434-acre Fort Sam Houston, which currently hosts the Army Medical Command and the headquarters of the Fifth Army, affords visitors an unusual opportunity to view the city’s military past; the first military flight in history took off from the fort’s spacious parade grounds, for example. Most of the historic buildings are still in use and thus off-limits, but two are open to the public. Located in the Quadrangle—an impressive 1876 limestone structure centered on a brick clock tower and enclosing a grassy square where peacocks and deer roam freely—is the Fort Sam Houston Museum, Building 16 (tel. 210/221-1886; free admission; Mon–Fri 10am–4pm, Sat noon–4pm). Its six rooms, containing some 8,200 artifacts, highlight the history of the armed forces in Texas, with a special focus on San Antonio. On 7 acres, the U.S. Army Medical Department Museum, 2310 Stanley Rd., Building 1046 (www.history.army.mil/museums/fieldMuseums/ameddmuseum/index.html; tel. 210/221-6358 or 210/221-0015; free admission; Mon–Sat 10am–4pm), displays army medical equipment and American prisoner-of-war memorabilia. The main building is a restored hospital train car. Note: Anyone wishing to visit the fort must get written permission from or be accompanied by a member of the DOD, whether active or retired, and come with a government-issued photo ID (such as a driver’s license). See the Joint Base San Antonio website (www.jbsa.af.mil/library/visitorinformation.asp) for the most up-to-date base entry requirements.