Americans paused Sunday to mark the fourth anniversary of the September 11th (2001) terrorist attacks that killed nearly three-thousand people. In New York, the names of the dead were read at the former site of the World Trade Center, destroyed when two planes hijacked by al-Qaida terrorists slammed into the two towers. Ceremonies were also held in Washington and Pennsylvania, where hundreds were killed in two other hijackings. At the White House, President Bush led the nation in a moment of silence at 8:46 am (EDT / 1246 UTC), the exact time when the first attack occurred. In Afghanistan, nearly 20-thousand American troops also marked the anniversary. Nearly four years ago, U.S.-led troops invaded Afghanistan to help topple the Taleban government that had given safe haven to al-Qaida. The terrorist group's leader, Osama bin Laden, remains at large.