Mayor Michael Bloomberg announced today that visitors to the 9/11 memorial next fall will have to reserve tickets in advance to see the site.

In an article today at DNAinfo.com, Julie Shapiro wrote that "memorial officials had previously described the 8-acre plaza as a new open green space for lower Manhattan, where local residents and workers could eat lunch and relax in addition to reflecting on the 9/11 attacks."

"But when the memorial plaza is scheduled to open on Sept. 11, 2011," the article continued, "it will be surrounded by construction, making it unsafe to allow free access, Bloomberg said," adding that "we anticipate having ticketing so we can control the number of people who go through security and get onto the plaza, so we don't have a crush." The mayor is also chairman of the National September 11 Memorial & Museum foundation.

The tickets would be free, and the memorial foundation has not yet decided how many people will be allowed in per day, a spokesman said, the article added, noting that Mayor Bloomberg said he anticipated "enormous demand." Memorial officials have previously said they expect 5 to 7 million people to try to visit the site in the first year it is open.

The memorial includes a tree-shaded plaza surrounding enormous waterfalls in the footprints of the original Twin Towers. By the 10-year anniversary of the attacks next fall, Mayor Bloomberg said he expects much of the plaza to be complete, along with the waterfalls and parapets inscribed with the victims' namesm, but construction of the 1,776-foot-tall One World Trade Center and Santiago Calatrava's winged PATH hub will be going on right near the memorial, which means that the only safe entrance and exit point will be West Street.

The mayor implied that he expected access to the memorial to be more open once the site is complete several years from now.

The 9/11 museum, scheduled to open in 2012, is also expected to require tickets.