Fort Woodbury was part of the Arlington Line, an extensive network of fortifications erected in present-day Arlington County, VA to protect Washington, D.C. from Confederate attack. Construction began on the Arlington Line in May 1861, shortly after war broke out, and accelerated after the Union’s defeat at the First Battle of Bull Run in July 1861. It stood atop one of Arlington’s highest hills, and was named for Major Dwight P. Woodbury, the engineer who designed and constructed the Line.

from Wikipedia