VIDEO: Somber memorial mark 11th anniversary of 9/11 terrorist attacks

Jeremy Hamilton places a U.S. flag next to a memorial bearing two pieces of steel from the World Trade Center in Weehawken, N.J., across from the skyline of New York, Sept. 11, 2012. Thousands will gather in New York, Washington and Pennsylvania to mark t

Across the Northeast United States and all across the nation, people gathered Tuesday to mark the 11th anniversary of the terrorists attacks of Sept. 11, 2001.

About 3,000 people died in the attacks, which took down both towers of the World Trade Center in New York City, as well as a separate attack on the Pentagon in Washington. A fourth plane crashed in a field in Pennsylvania after passengers retook control of the planed and thwarted the terrorists' attempt to crash it into a government building in Washington, D.C.