NEW YORK—In Manhattan’s financial district, the mood was visibly nervous Monday, as many workers returning for the first time repeatedly cast looks skyward at the gulf of light where the World Trade Center used to be.

Set against an otherworldly terrain of rubble and soot, a pedestrian-cluttered Wall Street seemed more like the hub of an authoritarian state than the financial capital of the world.

Jeeps hugged the sidewalks, hordes of journalists catching the spectacle snapped photographs from behind strict police barricades and fully-armored, camouflaged National Guard troops checked identifications at all subway exits.

Bigangi, 49, an office manager of a Wall Street bank who wished to be identified only by his last name, said that although he was not frightened to return to work, he was glad for the heightened security in the area.

“You just don’t expect something like that to happen to civilians,” he said, “Evil can strike at any time, so you have to be prepared.”