The area known as Arlington, Virginia is technically not a city, but a county. Thus, its full name is Arlington County, Virginia. Arlington County has no incorporated towns, owing to a Virginia law that states that no new municipality may be created in a county of a population density of more than 1,000 people per square mile.

    The county was originally part of Fairfax County, in the Colony of Virginia. When Washington, D.C. was created by decree of the United States Constitution, the area today known as Arlington was incorporated into it, and was known as Alexandria County of the District of Columbia. In the 1840s, Alexandria County was a large slave trade port, and partly because of this there grew a movement to return the county to Virginia. This was accomplished in 1846. The city of Alexandria, Virginia was carved out of Alexandria County in 1852, and the rest of the county was renamed Arlington in 1920 to avoid confusion. Thus, the present-day Arlington is the leftover portion of the former Alexandria county that was not incorporated into Alexandria.

   Arlington National Cemetery was officially designated a military cemetary in 1864, and stands on property formerly belonging to Civil War General Robert E. Lee. Today, it is the second largest cemetery in the United States, and houses the remains of war veterans from all of the United States' conflicts.

   The Pentagon, completed in 1943, is the world's largest office building, and the headquarters of the United States Department of Defense. On September 11, 2001, it was struck by American Airlines Flight 77 after being hijacked as part of the September 11, 2001 terrorist attacks.