According to Oxford professor of religion Diarmaid MacCullough, the reason Christianity has been able to grow and flourish when so many other religions withered and died away has been its ability to adapt.

That's the theme of this six-hour history, originally shown on the BBC. MacCullough, an affable and able host, literally walks us through Christianity's history, visiting all the important sites, interviewing most of the important figures and presenting us with a picture of what happened, why it happened and how it could have all been different. Even if you have no interest in religion, it is a fascinating story and MacCullough does a great job of telling it to us, while the visuals make it real. For example, when you see the actual church door where Martin Luther nailed his theses, you can't help but understand the Reformation a little better.

Each of the six DVDs contains a one-hour episode and tells a different part of the story. The first discusses the rise of Catholicism, demonstrating that after Christ's death, while Paul marched west to bring the message to the Roman Empire, Peter went east into Asia. At one point, more than 600 Christian churches flourished in the Asian countries, extending into China. Despite the attempts by the 20th-century Chinese government to stamp out the religion, it survived by going underground, and some of the original Christian churches in the country, built centuries ago, still exist and are used. Had things gone just a little differently, the center of the Christian religion might today be in Baghdad instead of Rome.

But things did not go differently and Western Catholicism triumphed. Today, more than one billion members of the religion look to Rome, half of all the Christians on the planet.

In the beginning, there was not the Church, the institution. Instead, there were the churches, more than 600 different denominations of Christians, all believing different things, all worshipping and living differently. To see how one branch, the Roman Catholics, systematically incorporated or triumphed over the others makes a fascinating story and shows the power of what a group can accomplish if they can get the established power structure on their side. How the early Christians went from preaching the virtues of poverty and from being martyred by the Romans to the richest and most powerful religion, the official religion of the crowned heads of Europe, makes a tale worth seeing and hearing.

From Rome, MacCullough skips to Eastern Europe where he examines the Eastern Orthodox sects that dominate the Balkans and Russia. Many have tried to stamp out Orthodoxy -- the Catholics, the Nazis, the Communists -- but the church refuses to go away. Despite all of the attempts to squelch it, today it has more than 150 million members worldwide. The show examines the qualities that allow the Orthodox to hold its influence despite governments, war and revolutions.

Then it is back to Europe to trace the rise of the Reformation. Catholicism relies on authority and obedience. Some people have a problem with that. Blind obedience and passive acceptance of authority can go against the individual conscience -- especially when the group we are supposed to obey and whose authority we are supposed to accept are participating in practices like selling indulgences, certificates which are supposed to shorten your time in Purgatory. The Reformation insisted the individual conscience was primary and that existing practices of the Catholic Church had to change or people would leave the church. Protestantism was, of course, the result. It was a result that spread Christianity into the New World as Protestants had to leave Europe to escape persecution.

With Protestantism established, it's a short leap to Evangelicalism. If you associate the Evangelical movement with Conservative politics, the radical right and all of that, this episode will convince you that you've missed the boat. Certainly, some American Evangelicals are associated with Conservative causes and certainly some buy into the current radicalism, but the movement is actually much more complex than that. It began with a concern for social justice for all people and stakes its claim that a direct and loving relationship with God was not only possible but essential. It's a worldwide movement; more than 50 percent of the population of Africa, for example, is Evangelical. American slaves were turned onto Evangelicalism and when, they were freed, many returned to Africa, taking their religion with them, and succeeded where white missionaries had failed in building Evangelical congregations. It is also very prominent in Asia and in Korea.

The final episode takes its title from an essay by C.S. Lewis, "God in the Docks," which means, of course, God put on trial, as religion was by science. MacCullough asks how and why, after centuries of conflicts with science and tacks by people such as Newton, Voltaire, Darwin, Spencer and the rest, Christianity has not died out but instead has shown a remarkable ability to adapt to the times and continue to make itself important. His conclusions are too complicated to summarize here but its ability to adapt and transform itself is crucial.

It's important to note that MacCullough describes, rather than proselytizing. He does not advocate. Instead he is an excellent historian, presenting the facts, tracing the actions and the reasons behind them without ever suggesting that the Christian religion is any more than another organization to be examined and understood. Whatever your belief or lack of beliefs, you will not find them attacked or endorsed here.

You will, however, have a better understanding and you will have been fascinatingly entertained. A History of Christianity belongs in every library, every church, every civic organization and the homes of everyone who wants to understand something about the society he or she lives in.