Left: On Sept. 11, emergency workers attend to the Pentagon after a hijacked American Airlines jet slammed into the building, killing 64 people aboard
the aircraft and 125 working in the building.

Right: Damaged portions of the building were rebuilt within a year of the attack. An area adjacent to the building is now the site of the Pentagon Memorial, which was completed in 2008.

SOURCES: Staff reports; PHOTOS by Rich Lipski, left, and Patterson Clark, right - The Washington Post.

Left: After being sent home following the terrorist attacks, government workers stream onto the Mall along 14th Street NW.

Right: On normal weekday mornings, the Mall is populated mostly by tourists.

SOURCES: Staff reports; PHOTOS by James M. Thresher, left, and Patterson Clark, right - The Washington Post.

Left: On the afternoon of Sept. 11, blood donors queue up in front of the Red Cross blood donor
center at 1915 I Street NW.

Right: The donor center has since closed. A restaurant now occupies the space.

SOURCES: Staff reports; PHOTOS by Kevin Clark, left, and Patterson Clark, right - The Washington Post.

Left: In the early afternoon of Sept. 11, police and Secret Service agents frisk and search a Pakistani-American couple who were driving a car with New Jersey license plates.

Right: Freedom Plaza, at the intersection of 14th Street NW and Pennsylvania Avenue.

SOURCES: Staff reports; PHOTOS by Michael Temchine for The Washington Post, left, and Patterson Clark, right - The Washington Post.

Left: An early-morning view of damage at the Pentagon on Sept. 12, 2001.

Right: The sun rises on a restored Pentagon.

SOURCES: Staff reports; PHOTOS by Tracy A. Woodward, left, and Patterson Clark, right - The Washington Post.

Left: Once one of the busiest sections of Pennsylvania Avenue, three blocks of the street in front of the White House were permanently closed
to traffic in 1995.

Right: The street's hinged barricades were replaced with retractable bollards in 2004. Granite pavers have replaced the old asphalt pavement.

SOURCES: Staff reports; PHOTOS by Robert A. Reeder, left, and Patterson Clark, right - The Washington Post.

Left: In 1983, Jersey barriers were placed along Pennsylvania Avenue in front of the White House. Those were removed in 1988 and replaced with bollards, which became a favorite perch for visitors.

Right: By 2004, a major renovation resulted in a more open and inviting public space. Removable and retractable bollards were confined to entry and exit points on the avenue.

SOURCES: Staff reports; PHOTOS by Robert A. Reeder, left, and Patterson Clark, right - The Washington Post.

Left: Until 2000, visitors were free to climb to the top of the steps at the Capitol.

Right: While visitors may still stroll around the base of the Capitol, they may no longer ascend the steps, where heavily armed guards are now stationed.

SOURCES: Staff reports; PHOTOS by Michael Robinson-Chavez, left, and Patterson Clark, right - The Washington Post.

Left: Participants in the Million Family March congregate on the steps of the Lincoln Memorial.

Right: Just before Independence Day, 2002, U.S. Park Police installed security cameras on the cornice of the memorial to keep an eye on the mall crowd.

SOURCES: Staff reports; PHOTOS by Bill O'Leary, left, and Patterson Clark, right - The Washington Post.

Left: Visitors navigate through a series of Jersey barriers and fences to reach the Washington Monument. The barriers were put in place in August 1998 as a precaution after the United States attacked terrorist targets in Afghanistan and Sudan.

Right: By July 2005, the concrete barriers were replaced by interlocking rings of distant, low granite walls. After an earthquake cracked the top of the monument on Aug. 23, a fence was installed to exclude visitors from the base of the monument.

SOURCES: Staff reports; PHOTOS by Shawn Thew for The Washington Post, left, and Patterson Clark, right - The Washington Post.

Left: A passenger sends his baggage through an X-ray machine at Dulles International Airport.

Right: Passengers must currently remove their shoes when passing through airport security, but that requirement may eventually be lifted.

SOURCES: Staff reports; PHOTOS by Gerald Martineau, left, and Patterson Clark, right - The Washington Post.

Left: An aerial view of the western face of the Pentagon, eight months before the attack.

Right: A repaired building looks out over the Pentagon Memorial, which opened to the public on Sept. 11, 2008.

Images courtesy of Pictometry

Left: Section 60 at Arlington National Cemetery is a final resting site for veterans from World War II,
Korea and Vietnam . . .

Right: . . . but it is also the area reserved for burial of military personnel killed in the Iraq and Afghanistan wars.

Images by GoogleEarth.