"How did the Mediterranean world become predominantly Christian?" asks historian Adam Schor of Long Island University, in Brookville, N.Y., in the current Journal of Religious History. "Generations of scholars have approached it, but each new theoretical angle seems to reopen basic questions."

Christianity spread throughout the Roman Empire, of course, after the death of Jesus around 33 AD, moving from a persecuted minority in the time of the Roman emperor Nero in 64 AD (blamed for Rome's most famous fire), to state religion with the Emperor Constantine's victory in 312 AD. But how — and how much — the early church grew in that time-frame remains a mystery, Schor notes, one that scholars have solved in widely divergent ways, starting in 1997 with sociologist Rodney Stark's book, The Rise of Christianity, with similarly conflicted answers.

"Appearances have deceived us here in many ways," Schor writes, looking at the various approaches since then that try to explain the growth in the Christian population. "Without concrete data, none (of the approches) truly counts early Christians." But, he suggests, each one may tell us something interesting. Past attempts include:

•The "mission" model, where "the rate of conversion (to Christianity) depends on the number of leading clerics and holy people," yielding a slowly accelerating curve of growth for the early church. The only problem is that by changing just a few numbers, say how many people your typical holy person converts every year, estimates will range for the early church having anywhere from 5.47 million to 15.8 million people by 350 A.D. (where the total population is no higher than 50 million.)

•The "values" model, where Christians taking to heart the advice to "be fruitful and multiply"led to exponential growth. Roman practices meanwhile, including infanticide, kept pagan population low. As well, Schor says, "values could influence conversion. Early Christians may have been vilified, but their values won admiration, even from some persecutors." In this model, early Christian numbers grow like microbes in a Petri dish, bringing about an even bigger range than the first model — from 3.5 to 34 million by 350 AD, depending on conversion rates.

•The "social" model, where every exposure to an early Christian is seen as possibly leading to a pagan converting, much like the chances of catching a cold. Diddling the conversion contagion odds coughs up estimates ranging from 3 to 20 million Christians by 350 A.D.

"Together, these efforts illustrate how careful modeling can help us to envision religious change in the Roman world. But they also reveal the limitations of modeling," Schor writes. "These models cannot tell us how many Christians there actually were. They can, however, help to investigate the factors that scholars have suggested drove conversion."

A new approach, he suggests, might borrow a kind of model popular with epidemiologists studying disease outbreaks called "network" analysis. Network analysis mathematically models each person as a node connected to others by bonds whose strength can vary by any number of factors, from family relationship to social status. That might account for life in the complicated Roman era, where status varied with wealth, citizenship, rank, occupation and reputation. "Network-based modeling thus offers a new (though still limited) path in the study of religious change," Schor concludes.

Of course, there's a drawback, he adds. "Realizing its potential, however, requires a technique unfamiliar to most historians: computer simulation." Even historians can't escape the computer era, it seems.

On the plus side, author Dan Brown may set his next thriller around a team of crack historians plundering a supercomputer to run historical simulations. Call it The Da Vinci Computer Code and we may have Hollywood's next blockbuster.

Enlarge By Simon Mein, Columbia Pictures Audrey Tautou and Tom Hanks in a scene from the motion picture "The Da Vinci Code."