And Cahill's books aren't just popular -- they're also popularizations through and through. He's the Carl Sagan of world history, distilling ideas from impenetrable scholarly work and presenting them with vivid prose.
True to form for a popularizer, Cahill has tackled big topics and drawn unapologetically broad conclusions. "It's nervy to say that you're writing about all of Western civilization. It's presumptuous, but who cares?" he said.
By failing to think big, he said, most modern historians have missed seeing the larger picture. "They keep insisting on carving history up into smaller and smaller units," he said. "It seems to me that it's also important to show developments over centuries and centuries of history."
"The Gifts of the Jews," for instance, covers three millennia. When you're going to tell in only seven books how the world came to be the way it is, you've got to press the fast-forward button and keep it brief -- his longest book so far is 350 pages.
To avoid being long-winded, the model Cahill keeps in mind is a childhood recollection -- Walt Disney nature films, which used time-lapse photography to depict the growth of a flower from bud to bloom.
"Human developments -- cultural developments -- are very, very slow," he said. "The really deep developments can take hundreds of years. And there are seeds of developments being sewn now that we don't even know about."
With three books down, Cahill is racing to the conclusion in the seventh "Hinges" volume, which will deal with the inception of the United States. "American democracy, to me, puts the last building block in place," he said.
That book is still years away, and three more lie between it and the most recent, "Desire." Subtitled "The World Before and After Jesus," "Desire" has a scale only slightly less sweeping than that implies. "Did he make a difference?" Cahill asks in the preface. It's a huge question, and Cahill's answers are interesting, though conventional.
That's not to say he always takes the middle road. "There are things that drive people crazy in these books. You know, 'How dare he write these things!' I used the words 'fuck' and 'shit.'"
An element of righteous irritation entered his voice as he defended his authorial choices. "Why shouldn't I write in the language people use? Doesn't everybody say these things?"
Cahill was pretty sure Jesus would have used those words, too. "I don't really see the point of reverence anyway. I don't think Jesus wanted to be treated with reverence. There's nothing in the gospels to indicate that he wanted to be treated differently than anyone else," he added. "A lot of the reverence (Christians practice) is a way of avoiding dealing with the ideas."
The ideas Jesus taught, Cahill said, mostly involve helping the underprivileged. "Why aren't these people who are kneeling down in churches going out and looking for Jesus in the poor? He assured us that's where he could be found."
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The irritation in his voice had changed to a sort of baffled disappointment in the failings of modern religious practice. "(They go to church instead) because it's a lot easier to go to church," he said.
Whenever someone criticizes others' religious dedication, they often sound hypocritical. But Cahill's personal assistant, Diane Marcus, said Cahill indeed practices what he implies in his books. "He's very concerned for people's rights, especially those that are downtrodden," she said. "He reads to people with AIDS every Wednesday night."
Those experiences led Cahill to write an op-ed piece for The New York Times that ran Easter Sunday of 2000. The paper altered Cahill's original title, "Things That Can Be Seen in the Dark," to "Changed."
Marcus said the revised title is fitting.
"I think the humanity of people is increasing thanks to his lectures and his books," she said. "And I believe that the world is the better for it."
The Arts & Entertainment Editor can be reached at firstname.lastname@example.org.