NEW YORK (AP) — More than 4 million people have visited the Sept. 11 memorial at the World Trade Center since it opened last summer on the 10th anniversary of the terror attacks.

The National September 11 Memorial & Museum announced the milestone Thursday.

The nonprofit foundation says visitors have come from all 50 states and 170 countries to see the two giant reflecting pools ringed by waterfalls that make up the memorial.

Memorial President Joe Daniels says all those visitors are helping to preserve the memory of those who died.