NEW YORK (AP) &045; The tourists from California peered through the slats of a metal fence surrounding the World Trade Center site, looking down into the nearly empty 16 acres for a sign of what happened here on Sept. 11, 2001.

Four years after terrorists hijacked jetliners that destroyed the twin towers, Steve and Marta Pilling thought they would find a memorial, something more than the names of the 2,749 victims on panels attached to the fence.

&uot;This reminds me more of a construction site,&uot; not the ground zero etched in Americans’ consciousness, said Steve Pilling of Murietta, Calif.

The fact that the downtown Manhattan site is both has driven a rebuilding process fraught with delicate negotiations and often competing passions of politicians, developers, architects and family members.

&uot;It’s the most emotionally charged building project in the world,&uot; said Robert Yaro, head of the Regional Plan Association advocacy group in New York.

Common ground at ground zero has been hard to find: Ambitious, thoughtful plans for everything from a 1,776-foot tower to a performing arts complex are on paper, but construction on most buildings has yet to begin.

On Monday, a day after a ceremony marking the fourth anniversary of the attacks, work is starting on one major project: a $2.2 billion transit hub that replaces a temporary station that opened in 2003.

Leaders of the process say a remarkable amount has been accomplished, and that rebuilding a site like this is unprecedented.