Roads in the Shenandoah Valley, during the Civil War
Source: Library of Congress - Vicinity of Winchester and Harper's Ferry, Va..
The cities in the valley developed initially as the sites selected for county seats, the administrative centers for government. They simultaneously served as the "central places" with specialized services to support the local farming community, plus the transportation of people and agricultural products from the valley to Baltimore and Philadelphia. Further south, Salem and Bristol also supported travelers as well as local farmers.
Look at Route 250 on the map of Virginia, from the West Virginia border to Richmond. You don't need to be an "A" student to see that the small communities of Monterey in Highland County, Zion Cross Roads in Fluvanna County, and Gum Spring in Goochland County might owe their existence to being at the intersection of two roads. The harder question is - why didn't these communities grow into a city as large as Staunton or Charlottesville? Or follow US29 north from the North Carolina border. Between Danville and Lynchburg are the small communities of Chatham in Pittsylvania County and and Altavista (on the Roanoke/Staunton River, not the search engine on the Internet) in Campbell County. Clearly, not every community is destined to grow into an urban center.