Surrounded by the Blue Ridge Mountains at the confluence of the Potomac and Shenandoah Rivers, Harpers Ferry thrived as an industrial community during the first half of the 19th century. By 1860, nearly 3,000 residents lived in the Harpers Ferry area, and its Federal armory produced more than 10,000 weapons per year. When civil war erupted in 1861, defending Harpers Ferry became strategically important to both North and South, and occupying and defending this border area required fortifying the surrounding heights. Both Union and Confederate armies found this difficult as Harpers Ferry changed hands eight times between 1861 and 1865.