The tallest building in the United States, the Willis Tower in Chicago, Illinois, stands 1, 450 feet high.

CNN: STORY HIGHLIGHTS

The tower's builders say it will surpass Chicago's Willis Tower as the tallest building in the United States, with a final height of 1, 776 feet -- a nod to the year of the Declaration of Independence.

CNN: Obama signs beam of One World Trade Center

Draper was there, in the holding room of the elementary school, as Bush and his advisers first saw the second plane, United Airlines Flight 175, crash into the south tower, hitting it between the 77th and 85th floors.

CNN: STORY HIGHLIGHTS

Seventeen minutes later, United flight 175 hit the south tower.

BBC: 9/11 debris found in New York identified as plane wing

According to the indictment handed up Thursday, a young man identified as Narseal Batiste, beginning in November 2005, recruited and trained the others "for a mission to wage war against the United States government, " including a plot to destroy the Sears Tower.

NPR: U.S. Arrests 7 Accused of Chicago Bomb Plot

As usual, the event's proceedings will pause six times to commemorate the moments each tower was struck and fell and the moments the Pentagon was struck and United Airlines Flight 93 crashed to the ground in Pennsylvania.

WSJ: Politicians Silenced at 9/11 Event

As soon as my brain had a scant few seconds to take in what was happening, hijacked United Airlines Flight 175 flew into the South Tower.

FORBES: Birth, Death and 9/11

Marwan al-Shehhi is thought to have piloted United Air Lines Flight 175 into the World Trade Center's south tower.

CNN: Uncle calls hijack suspect 'innocent passenger'

Long before he became the bleeding edge of the green building industry, David Borchardt, the Chief Sustainability Officer at Rockville, MD-based Tower Companies, earned his spurs cleaning up many of the most polluted Cold War weapons sites in the United States.

FORBES: The Towering Heights of Green Building