BILL MOYERS: Thomas Cahill has taken on a task as daunting as when 18th century historian Edward Gibbon tackled The History of the Decline and Fall of the Roman Empire in six volumes. Or when Thomas Carlyle published his three-volume history of the French revolution in 1837, the first book of which he had to rewrite from scratch after the manuscript was accidentally burned by a servant.

Over the past two decades, Tom Cahill has been writing a series of books he calls The Hinges of History, critical moments in Western civilization brought to life through the stories of individuals whose words and deeds helped make us who we are today.

The first, How the Irish Saved Civilization, was on the New York Times bestseller list for nearly two years and each subsequent volume has been an international success.

His latest, the sixth in a projected series of seven, is Heretics and Heroes: How Renaissance Artists and Reformation Priests Created Our World, and has just been published.

Recently, Tom Cahill and I spoke about the book in a conversation that ranged from Christopher Columbus and the bubonic plague to the nature of faith and human progress.

BILL MOYERS: So answer a question you've been asking several times recently in your various writings. What is the purpose of religion?

THOMAS CAHIL: I don't think it has just one purpose. I think it has several purposes. At the deepest level, it's about an entrance to another world than the one that we know. It has to be an insight into something beyond the present physical moment. And I think that's true of any religion. I'm not just talking about Christianity now. If it doesn't have that, it's not going to survive.

And it's only a religion with that mystical dimension that does, in fact, survive. Beyond that, the taking care of human beings who don't have anybody to take care of them is the task of Christianity. And of every religion, I think. It, if you find a community that has a mystical sense of who they are and what they are not, and a community that actually cares for those in need, you've found what you need to find.

BILL MOYERS: You have written on other occasions, that good religion is almost always mystical. And by mystical, you mean?

THOMAS CAHIL: It gives you an insight into something beyond our physical reality. You and I are sitting here talking, there are cameras, there are guys and men and women back there who are part of the crew. You know, we're just part of the, this physical reality. But we also know that there are things going on between us that cannot be accounted for simply by physical reality.

You know, you can say it's just psychological, or you can say it's deeply spiritual. There are things that we don't know how to account for that we experience. And those are in some way experiences of God. However provisional they may seem.

BILL MOYERS: Well, they're always provisional I think because we never know.

THOMAS CAHIL: That's right.

BILL MOYERS: I guess that's where faith comes in?

THOMAS CAHIL: Yup.

BILL MOYERS: There's a debate of a sort going on in a certain philosophical corner over the notion that the very idea of progress, about which you write in here consistently, that the very idea of progress is a pipe dream. The British philosopher John Gray, you may have been reading him, argues that human flourishing, of which there are many examples in your book, is cyclical.

That it's not inevitable. That we never get there. And in fact, often one reverses after another. The American experience and the American independence from Britain was followed by a God-awful civil war. The slave were freed only to be subjugated by another form of coercion.

There were great strides made in technology, in science, in the 19th century, followed by horrible world wars in the 20th century. And John Gray concludes from his looking at history and at human nature that faith in progress leads to great disasters in crimes. Did you find that in writing Heretics and Heroes?

THOMAS CAHIL: I think that Gray has at least half of it right, but not necessarily the whole thing. We are not the, our history is not simply a history of progress. There's plenty of regress in our history, where we go backwards. Where we came forward and then go backwards. It happens over and over again.

I would say that it just not but I don't think it's cyclical. It's not that, oh, here we are again. We're back in ancient Mesopotamia. You know, we're not. We're not. But that doesn't mean that the great advances that we refer to in our own history, invention of democracy, the end of slavery, the defeat of the Nazis who almost took over the whole world, it doesn't mean that those things are either inevitable or will be followed by more triumphs.

They can just as easily be followed by disasters and defeats. There's no guarantee that we will progress. But that doesn't mean that we simply fall backwards. That it's not as if the entire experience of human lives is like the experience of the season, summer, fall, winter, spring, summer, fall, winter, spring, over and over again.

I don't think our experience is cyclical in that way.

BILL MOYERS: I was gripped by your section here on the Black Death, the great Bubonic Plague the struck Europe in 1347, killed about half of the population on the continent, and something like a hundred million people around the world. You describe it as swellings in the groin, an armpit grew to the size of an egg or apple and spread through the body.

Few of the sick recovered and almost all died after the third day. But here's the passage that struck me. Quote, “human compassion and fellow feeling[s]…” were, “cast aside.” “People abandoned their holdings; houses became common property, and ‘reverence for law, whether divine or human…’” finally “disappeared.’"

THOMAS CAHIL: Well, just think about it for a minute.

You live in a little town and half of the people you know are dead. And you look around, and there's a lot of empty space all of a sudden. My neighbor on the other side of the road is gone, so is his whole family, and his fields are lying fallow. Why don't I just take them over? Why don't I just add to my spread?

And you have things like that going on all over the place in the period after the beginning of the Black Death. The Black Death didn't end easily. It starts really in the middle of the 14th century and keeps going. The, and out of that came a new kind of human being.

And one of the first people that I acknowledged as being that new kind of human being is Columbus. Columbus is a guy who has no, he has no roots, he has no, he's nobody. But he, he's a great traveling salesman. He's also the archetype of the traveling salesman. He goes from one European court to another, charms the sovereign who says, yeah, this sounds great. Maybe I could invest in this and really make a bundle.

And then he turns it over to the wise men of the court who's read everything that Columbus has read and a lot of other things and they come back to the sovereign and say, this is not an investment opportunity. This guy's a crackpot. He doesn't know what he's talking about. He doesn't, his measurements are all off. And they were.

But Columbus did know one thing, which almost no one knew at the time, which was the direction of the trade winds over the Atlantic. So that he sets out south and it comes back north, which as we know, is the way they go, the counterclockwise. But nobody knew that at the time. How did he know that? We have no idea. But he did. Of course, he didn't make it to China. And in fact, any sailor who claimed that they had found a new continent, was, had his tongue cut out.

BILL MOYERS: As a heretic?

THOMAS CAHIL: No, just as somebody that Columbus didn't approve of. He was not a nice guy. But he definitely, a sort of avatar of the new man that occurs in this period when there was so much emptiness and therefore so many opportunities for so many people.

BILL MOYERS: There's a paradox there, because and you write about this, that as the natives in this newly-discovered new world, were horribly treated, made slaves, tortured, put to death, the philosophers, some of the philosophers and the poets and some of the priests in Europe were writing, talking about a new Eden.

THOMAS CAHIL: Right, right. And it opened up the idea really of utopia even before Thomas Moore, who writes the book. You have people saying, well, who knew there were people like this, you know? They don't have any clothes.

Could they be the children of Adam and Eve before the fall? Could they be superhuman? Well, all of these thoughts are happening in Europe while the American natives are being killed.

And made to work in gold mines that don't produce any gold. And all sorts of horrible things like that. But the discovery of America touches off new ways of thinking in Europe. And especially new kinds of theology. well, is God completely different from who we thought he was? If the world is actually like this.

BILL MOYERS: It was interesting to me to be reading about the Black Death, you go a few more pages along, you read a lot of and suddenly there's this great art. The contrast between the portrait you draw in words of the Bubonic Plague, the Black Death, and these powerful expressions of human creativity. Really touching.

THOMAS CAHIL: Well, it's a renaissance. A renaissance is the art. There is no renaissance without the art. I, to me, that's the, of course, music was important and literature as well. But the overwhelming factor was art, both sculpture and painting, though especially sculpture.

No one knows why the Renaissance happened. We know certain causes. We know that people were rediscovering the past, were rediscovering the Greco-Roman past, the classical past. It's starts with people collecting old manuscripts that nobody had seen in a very long time. People rereading Virgil and Cicero for the first time in centuries.

And then realizing that the real parents of this period are the Greeks. And going back and then beginning to read Greek. No one had read Greek in Western Europe for more than 1,200 for almost 1,200 years. No one. So no one had read the New Testament in its original language. The, but the, they begin to dig up old statues. And they begin to look at what the Greeks and the Romans did with statuary, which had been completely forgotten.

Out of that comes Michelangelo and people like him. It's this incredible burst that seems to come from nowhere. But it doesn't come from nowhere. It does have a precedence. But they're kind of very small precedence given what you get out of them and it almost all centered around not just Italy, but the city of Florence.

BILL MOYERS: You've taken us on quite a journey.

THOMAS CAHIL: Yeah, well, it's a huge era to get through. And it has these two things going on. The Renaissance and the Reformation, which seems to have nothing to with one another, but both come out of the rediscovery of the classical past. And in the case of the Reformation, the rediscovery of the Greek New Testament. And people reading it again for the first time in 1,200 years. And the Renaissance is a rediscovery of the art and literature of the Greco-Roman period. And so the Renaissance and the Reformation go in two completely different directions. But they start in the same soil.

BILL MOYERS: What's next? America, the age of technology, Google, Facebook--

THOMAS CAHIL: Well, there's the, there's one more book.

BILL MOYERS: What is it?

THOMAS CAHIL: I think I have to go from the Enlightenment to the present. The, that's what I have in mind. As Lady Bird Johnson used to say, the Lord willing and the creeks don't rise.

BILL MOYERS: The book is Heretics and Heroes. Thomas Cahill, thank you very much for being with me.

THOMAS CAHIL: Thank you, Bill.