The theme of Mr. Moses’ speech was a bitter one: the ingratitude of the public toward men who had done so much for the public. “Some day,” he said, “let us sit on this bench and reflect on the gratitude of man.”

In front of me the row of gray heads nodded in appreciation. “‘R. M.’ had built so much, created so much,” they whispered to one another. “Why didn’t people understand? Why weren’t they grateful?”

Why weren’t they grateful? As I recalled that Exedra scene in 1969, as I was trying to organize my book, I suddenly knew, all in a moment, that that question would be its last line. For the book would have to answer that very question, would have to answer the riddle posed by the Moses Men: How could there not be gratitude, immense gratitude, to the man who had dreamed a great dream — of Jones Beach and a dozen other great parks, and of parkways to reach them — and who to create them had fought, and won, an epic battle against Long Island’s seemingly invincible robber barons? How could there not be gratitude to the man who had built mighty Triborough, far-­stretching Verrazano, who had made possible Lincoln Center and the United Nations? And yet there were ample answers to that question. Did I think in that moment of Robert Moses’ racism — unashamed, unapologetic? Convinced that African-Americans were inherently “dirty,” and that they don’t like cold water (“They simply didn’t like swimming unless it was red hot,” he explained to me confidentially one day), he kept the water temperature deliberately frigid in pools, like the ones at Jones Beach and Thomas Jefferson Park in Manhattan, that he didn’t want them to use. Did I think of the bridges he built that embodied racism in concrete? When he opened his Long Island parks during the 1930s, the only way for many poor people, particularly poor people of color, to reach them was by bus, so he built bridges over his parkways too low for buses to pass. Or of the “slum clearance” projects he built that seemingly created new slums as fast he was clearing the old, or of the public housing he placed in locations that cemented the division of New York by race and class? Did I think in that moment of the more than half a million people he dispossessed for his projects and expressways, using methods that led one observer to say that “he hounded them out like cattle”? Did I think of how he systematically starved New York’s subways and commuter lines for decades and blocked proposals to build new ones, exacerbating the region’s dependence on the automobile? I don’t remember exactly what I thought of when I remembered Robert Moses’ speech at the Exedra — only that in that moment, seeing the book’s last line, I suddenly saw the book whole, saw the shape of everything that would lead up to that line. I began organizing the book, the thoughts coming faster, I recall, than I could write. Over the next days, I outlined the book — in a quite detailed outline — from beginning to end. Some parts of what I wrote from the outline would later have to be truncated or cut out entirely so that the book could fit into one volume; aside from these deletions, “The Power Broker” as it was published follows that outline all the way through. The moment, of course, occurred a long time ago — so long ago, in fact, that when I reread the book this year, I at first got its date wrong, thinking it had occurred while I was at the Exedra scene, and I wrote a note on the last page saying that. Only a few days later did I realize that the moment had actually occurred when, struggling to organize the book in 1969, some years after the Exedra ceremony, I remembered the scene. I had to change the wording of my note to make it accurate.

But the rest of the memory is clear. So I’m glad that this year I read “The Power Broker” again, at last. The moment when I thought of its ending — and of the shape of the book — was a crucial moment in my life. And I had forgotten it.