Most of the development of Eastern Fairfax County resulted after WWII. The post war baby boom caught Fairfax County scrambling to build housing for our returning war heroes. Eastern Fairfax County is mostly defined by Alexandria, Belle Haven, Historic Mount Vernon, Fort Belvoir and Gunston. North and Western Fairfax County communities include Falls Church, McLean, Great Falls and Herndon. The County offers many notable planned communities such as Fairfax Corner, Laurel Hill, Burke, Reston and Kingstowne to name a few. The Tyson’s Corner area of Fairfax County is Virginia's largest office market and the largest suburban business district in the nation. The county maintains many miles of bike trails running through parks, adjacent to roads and through towns such as Vienna and Herndon. The Washington & Old Dominion Railroad Trail runs through Fairfax County, offering one of the region's best, and safest, routes for recreational walking and biking. In addition, nine miles (14 km) of the Mount Vernon Trail runs through Fairfax County along the Potomac River.