For me, the design of the 9/11 Memorial was really fundamentally about two simple ideas. One was about making absence visible and present, what is no longer here. And the other was this notion of a place of public assembly, a democratic, urban, civic public space where people could come together. I think both of those ideas came from direct experience of being here in New York during the attacks and then the aftermath that followed.

I started to think about a memorial, actually, a few weeks after the attacks, and at the time I couldn't actually imagine building anything on the site of the World Trade Center. It was a six-story high pile of rubble that was on fire, and bodies were being pulled out of it. And to me it was much too soon, much too raw a wound to touch. And so I was drawn, actually, to the Hudson River, which is a block to the west of the site. And I imagined the surface of the river sort of torn open, forming two square voids, and the water of the river rushing into these voids, into these big square holes, and failing to fill them up. All of this water flowing into these empty vessels, and they remain empty. There was a sense of continued absence, that sort of improbable, inexplicable tear in the fabric of the world. And it was sort of an impossible image to understand. How do you take water and tear it open like that? And I spent close to a year in my free time sketching and modelling, and eventually building a small fountain about a foot by a foot. They capture that idea of the surface of the water being shorn open, forming two square voids. And I took that little fountain and I brought it up to the rooftop of my apartment in the East Village, where I had seen the second plane strike the South Tower. And I photographed it against the skyline of New York, and I could see the absence of the towers in the skyline being reflected and mirrored in these two voids in the foreground. And I did all of this really for myself. It was a very self-directed, cathartic exercise that was a way for me to deal with what I had seen and witnessed.