Memories of that horrible day 11 years ago remain indelible.

Searing images of airplanes slamming into the World Trade Center, and the shock of innocent lives lost in a cloud of toxic dust and debris as the Twin Towers collapsed upon themselves, are forever imprinted on our soul. So is the heroic response of police, firefighters and ordinary citizens who set personal safety aside, converged on Ground Zero and threw themselves into the rescue, clean up and reclamation of the area.

The tragedy brought out the best of America as the public absorbed the unthinkable wounds in lower Manhattan, at the Pentagon and in a field in Pennsylvania, and met the challenge of caring for the sick, remembering the dead, defending the nation and rebuilding.

The latest example of a caring nation came yesterday when, after a long battle, federal officials finally announced that 50 types of cancer have appropriately been added to the list of diseases for which first responders at Ground Zero will be compensated.

The National September 11 Memorial opened to the public on 9/11 last year. Water cascades down the sides of two pools located in the footprints of the Twin Towers, and the names of 2,983 victims are inscribed on their parapets. But the rush to complete the memorial in time for the 10th anniversary of the attack led to cost overruns. Previous delays and political infighting over funding and oversight have stalled completion of the companion 9/11 museum seven stories below the memorial.

The agreement last night by New York City Mayor Michael Bloomberg, chairman of the National September 11 Memorial & Museum Foundation, and Gov. Andrew M. Cuomo, in his role with the Port Authority, is making progress toward resolving the impasse. Preserving and presenting the story of 9/11 is more important than any turf fight.

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While controlling costs is key, what needs to be done shouldn't obscure all that has been accomplished. Since 9/11, there hasn't been any similarly successful terrorist attack on American soil. We've had some close calls, for instance the Christmas Day underwear bomber in 2009 and the car bomb attempt in Times Square in 2010. And a U.S. Army psychiatrist and al-Qaida acolyte shot and killed 13 people at Fort Hood, Texas, in November 2009. But there has been nothing approaching the magnitude of the 9/11 attacks.

Osama bin Laden is dead, and al-Qaida has been scattered and degraded. The war in Iraq is over, and the one in Afghanistan will soon end as well. And after a determined effort to restructure federal agencies and harden potential terrorist targets around the country, we are safer today than we were on 9/11.

In lower Manhattan, the September 11 Memorial has drawn 4.5 million visitors since it opened a year ago. The signature 104-story skyscraper going up on the site is nearing completion. And the downtown area, revitalized with new businesses, hotels and residences, is bustling with life.

The tragedy of 9/11 will be remembered always, but the irrepressible spirit with which the American people met this historic test of national will should be too.