As the Duke of Gloucester said to Edward Gibbon on being presented a copy of "The Rise and Fall of the Roman Empire": "Another damned thick square book! Always scribble, scribble, scribble, eh, Mr. Gibbon!"

The same could be said of historian Diarmaid MacCulloch, the author of two other damned thick square books: a biography of Archbishop Thomas Cranmer, an Anglican churchman and martyr who gave the world the Book of Common Prayer; and an examination of the Reformation.

Now comes "Christianity: The First Three Thousand Years." It's a wide-ranging, inclusive look at the world's largest religion.

"In 2009, it has more than two billion adherents, more than four times its numbers in 1900, a third of the world's population, and more than half a billion more than its current nearest rival, Islam," MacCulloch writes.

At almost 1,200 pages and weighing close to 4 pounds, this volume is an excellent ad for digital books: This is heavy stuff, literally and figuratively.

Fortunately, it's also an eminently readable look at the religion that gave the world the concept of the ultimate equality of all individuals.

History has usually been taught from a secular perspective in recent years, without reference to the religious beliefs of the Puritan settlers of New England, or the religious motivations of the Abolitionists. More recent history — South Africa, the former Soviet Union and its possessions — has included religion only where unavoidable, in the influence of a Desmond Tutu or Karol Wojtyla.

That should change. Just before Christmas, the journal Inside Higher Ed reported that religion is now "the most popular theme studied by historians," surpassing cultural and social history, the previous front-runners. To understand and explain our world, it is still necessary to have a grasp of the importance of faith for most of humanity.

The title catches the eye: MacCulloch is including Greek culture and Jewish thought from the time of King David — a millennium before the birth of Christ. It's a cute idea, but those strains are more a prologue and foundation to the story of Christianity than a part of it.

Still, putting Christianity into a fuller cultural context is one of MacCulloch's most valuable contributions here. He not only explores what went before, but he examines, for instance, the rise of Islam and the story of the Mongols, and Christian reactions to them. The son of a vicar in the Church of England, he is no longer a believer but remains sympathetic to Christianity, calling himself "a candid friend" of the faith.

Most Westerners, not unnaturally, view Christianity through a Eurocentric lens. MacCulloch blasts that prejudice with a barrage of facts, demonstrating that the center of the Church could easily have been Baghdad instead of Rome.

He explores the various Eastern churches that established themselves as far away as China and India, and the different ways of viewing the nature of Christ: one nature or two, equal to the father or subordinate.

The tensions between outsider and insider status, between being persecuted and doing the persecuting, are explored; so is the shift, in Western Christianity, from prudishness about sex to outright hostility toward it.

MacCulloch methodically knocks the props out from under the idea that the Church in the West and its particular theologies have any realistic claims to primacy over the East. The often decidedly secular ways in which a succession of Bishops of Rome helped themselves to power and prestige, culminating in the late-blooming (1870) declaration of papal infallibility, are set forth chronologically.

"(The apostle) Peter's charisma was the most useful resource at the disposal of Roman bishops as, from the third century, they increasingly claimed to be arbiters of doctrine in the wider Church," MacCulloch writes. Historically, few popes were major theologians, so "the pope's claim to a special place in the life of the Church came rather from the tombs of the Apostles."

The tragic threads of anti-Semitism and inter-Christian strife are followed from their early beginnings. Cases of Christian victimization — the Armenian holocaust; the Huguenot, Cathar and other slaughters — get their due. Changes in theology and ritual are matched with their historical imperatives.

"Christianity" is full of fascinating facts: Marriage was considered a simple contract between two people for centuries, not a sacrament that concerned the church; the "mad monk" Rasputin, for all his faults, fits into a Russian Orthodox tradition of the "holy fool"; priests in the Latin Church were allowed to marry until the 12th century; the first cup of coffee in England was consumed by a Greek Orthodox priest at Oxford in the early 1570s.

It's been noted before that the Reformation was made possible by the invention of the printing press. MacCulloch adds that it caught on in the north, where Rome's indulgence-pushing "Purgatory Industry" was particularly oppressive.

MacCulloch's dry, ready wit is invaluable in guiding us through the masses of names, dates, places and theological concepts. We meet William Buckland, an Anglican clergyman and amateur scientist, "who kept a hyena at home as much for the enjoyment of its company as for research, and announced his intention of eating his way through the whole range of created animals."

The book has its faults, including issues with the index (potentially devastating in so massive a work), and MacCulloch is overgenerous in including some movements as Christian that grew in other directions from Christian roots: A belief in the existence of many gods should be a disqualifier.

The fall of Christendom (a word invented by an Anglo-Saxon monk in the 9th century) at the end of World War I has not meant the end of Christianity. It's still growing, and changing as it grows, and MacCulloch chronicles it to the present day. This fascinating exploration is worth the neckache that comes from hefting it.