Arlington National Cemetery Fast Facts

(CNN)Here's a look at Arlington National Cemetery in Virginia.

Facts:
Arlington National Cemetery in Arlington, Virginia, contains the remains of more than 400,000 people from the United States and 11 other countries, buried there since the 1860s.
More than three million people visit the cemetery annually.
    The Arlington estate was originally owned by George Washington Parke Custis, adopted grandson of George Washington. His daughter Mary Anna Randolph Custis, who married Robert E. Lee, inherited the estate. It was abandoned by the Lees during the Civil War and used as headquarters for the Union army.
    Arlington House (also known as Custis-Lee Mansion) is currently a memorial for Robert E. Lee and run by the National Park Service.
    Arlington National Cemetery is administered by the Department of the Army.
    Nearly 5,000 unknown soldiers are buried at Arlington National Cemetery.
    The cemetery has the second-largest number of people buried of any national cemetery in the United States. Calverton National Cemetery, on Long Island, near Farmingdale, New York, is the largest.
    Burial in Arlington is generally limited to active, retired and former members of the armed forces, Medal of Honor recipients, high-ranking federal government officials and their dependents.
    Funerals are normally conducted six days a week, Monday through Saturday. Arlington averages 27 to 30 funerals, including interments and inurnments, each weekday, and six to eight services on Saturdays.
    The flags in Arlington National Cemetery are flown at half-staff from a half hour before the first funeral until a half hour after the last funeral each day.
    The partial remains of the seven astronauts who died aboard the Space Shuttle Challenger on January 28, 1986, are buried at the cemetery.
    The seven Columbia astronauts have their own memorial at Arlington, near the one for the Challenger.
    As a living tribute, there are 36 Memorial Trees for Medal of Honor recipients.
    Annually, just prior to Memorial Day weekend, the 3rd US Infantry (The Old Guard) places American flags before the gravestones and niches of service members buried at Arlington National Cemetery and the US Soldier's and Airmen's Home National Cemetery.
    The cemetery has armed guards stationed throughout the grounds.
    Visitors to the cemetery are required to enter through one of four access points: the cemetery's main entrance on Memorial Avenue, the Ord & Weitzel Gate, the Joint Base Myer-Henderson Hall Old Post Chapel Gate, or the Service Complex Gate off of Colombia Pike.
    Visitors undergo security screenings and random ID checks.
    The Tomb of the Unknown Soldier:
    The Tomb of the Unknowns (aka Tomb of the Unknown Soldier) has never been officially named. It is a memorial to the dead of World War I, World War II, the