More than 12,000 people will gather at the Pentagon on Sept. 11 directly in front of the rebuilt wall where a hijacked plane hit a year earlier, a location chosen to send a message of defiance.

Organizers had initially intended to have the Sept. 11 observance on the opposite side of the 34-acre building, at the river entrance parade ground where ceremonies are customarily held, including October’s memorial service.

But they decided that the crash site was the more appropriate spot to remember the 184 victims, salute the rebuilding of the Pentagon in less than a year and send a message about the war on terrorism.

“The fact we’re holding the event at the site where they dared to attack us is a strong signal that yes, you fired a shot and the al-Qaida did a terrible thing, but we’re whole, and we’re coming to get you,” said Richard McGraw, the deputy secretary for legislative affairs at the Defense Department, who is overseeing the event.

The idea of returning to the scene of the terrorist attack, though, sent shudders through some victims’ relatives.

“I for one will not attend a memorial on the 11th at the Pentagon at the time of the first attack,” said Craig Sincock of Dale City, Va., whose wife, Cheryle, died in the Pentagon that day.

About 2,000 family members are expected to attend the ceremony, which is to feature an address from President Bush. The “great majority” of victims will be represented by family members, according to Meg Falk, coordinator of the Pentagon’s Sept. 11 family assistance. “Some indicated it was too much for them,” she said.

The decision to stage the Sept. 11 Pentagon ceremony at the impact site, which remains a construction zone, creates significant logistical challenges. The Pentagon could have accommodated 30,000 people at another entrance.