It is the sky that gives the game away. Suddenly it is there in wide-screen glory, cloud-free and defiantly sunny, where previously there had been only slivers and fragments of blue.
Emerging from the Wall Street subway station minutes earlier, I had felt that familiar rush of mild claustrophobia that can swamp you in Lower Manhattan – the vague sensation that you are walking on the bed of a huge upturned hairbrush, a giant cluster of bristles rearing above your head. But as I edge west along Liberty Street, I can see a clearing in this forest of skyscrapers, as if a wildfire, now extinguished, has scorched an ashen path.
Of course, that is exactly what happened here. And the wildfire that burnt a hole into New York’s Financial District on 11 September 2001 needs no explanation. You know where you were on that day, and how you saw it unfold – those incomprehensible hours of crashed planes and tearing metal, of flames and choking dust, of destruction and death.