Most monuments are stone and concrete — made to last forever. But the Bellevue Wall of Prayers, a makeshift bulletin board covered with images of those missing after the Sept. 11, 2001, World Trade Center attacks, is one of that day's most enduring symbols. Now preservation experts are trying to make this poignant memorial as permanent as granite.

The 170-foot-long, 8-foot-tall wall was created as New Yorkers in search of loved ones stapled and taped missing-person fliers to a plywood construction fence outside Manhattan's Bellevue Memorial Hospital.

“The fliers capture the victims' faces, names, places of work, descriptions of their appearance, clothing and personal histories,” says Museum of the City of New York (MCNY) <www.mcny.org> spokesperson Sarah Henry. Visitors added poems, candles, flowers and flags, and hospital staff hung signs bearing the name Wall of Prayers.