That first tower toppled at 9:59 a.m., a billion pounds of steel and concrete and bodies raining down. Smoke billowed like thunderheads, and New York’s mayor seemed to disappear into death’s maw.

Mayor Rudolph W. Giuliani was two blocks from the south tower, in an office on Barclay Street, trying to get the vice president on the phone, when his world went dark with smoke. Back at City Hall, Deputy Mayor Rudy Washington waited and wondered and dialed the governor.

“We really didn’t know what had become of the mayor,” he said. “I spoke to Governor Pataki, and we closed the schools and canceled the election.”