A good story on CNN to summarize it.

Relatives of September 11 victims bowed their heads in silence Tuesday to mark the moments exactly six years earlier when hijacked planes crashed into the World Trade Center, the Pentagon and a Pennsylvania field. The dreary skies created a grim backdrop, and a sharp contrast to the clear blue of that morning in 2001.

"That day we felt isolated, but not for long and not from each other," Mayor Michael Bloomberg said as the ceremony began in New York. "Six years have passed, and our place is still by your side."

Construction equipment now fills the vast city block where the World Trade Center once stood. Work under way for four new towers forced the ceremony to be moved away from the twin towers’ footprints and into a nearby park for the first time.