"How many people in your church would have to be pulled out and executed and tormented for it not to have a tremendous effect for many years on your memory and self-perception," Litfin says. "The early Christians are not foisting a narrative out of the blue about being matyrs."
The early Christians' secret weapon
Other scholars say it wasn't simply persecution that helped the church grow. Instead, they say, Christians had a secret weapon.
The martyrs may have gotten all the press, but it was ordinary Christians who got it done by the way they treated friends and strangers.
Life in ancient Rome was brutal and nasty, says Rodney Stark, author of "The Triumph of Christianity." Stark's well-regarded book gives one of the most detailed descriptions of the early church and ancient Rome.
Forget those antiseptic portraits of Roman cities you see in biblical moves such as "The Robe." Roman cities were overcrowded, raw sewage ran in the streets, people locked their doors at night for fear of being robbed and plagues were rampant. Soap had not yet been invented, Stark says.
"The stink of the cities in the summertime must have been astounding," Stark says. "You would have smelled a city miles before you got to it."
Christians stood out because they created a "miniature welfare state" to help the less fortunate, Stark says. They took in infant girls routinely left for dead by their parents. They risked their lives to tend the sick when plagues hit and others fled in terror. They gave positions of leadership to women when many women had no rights, and girls as young as 12 were often married off to middle-aged men, he says.
Ordinary Romans might have thought Christians were odd but liked having them for neighbors, Stark says.
"If people had really been against them, I don't think they would have grown like they did," Stark says.
Christianity became so popular that when Rome did unleash one of its sporadic waves of persecutions, the empire couldn't stop the church's momentum, Stark says.
"If you knocked off a bishop, there were 20 guys waiting to be bishop," Stark says
Christian belonging, not blood, is what drew many people, another scholar says.
The Easter story of a risen savior wasn't distinctive in Rome's competitive religious marketplace. Dying for one's beliefs wasn't considered heroic; it was expected in the Roman world, says Selina O' Grady, author of "And Man Created God: A History of the World at the Time of Jesus."
The early church, though, was radically inclusive. First-century Rome was undergoing globalization. The peace of Rome had made travel easier. People left homes and tribal ties for Rome. The empire was filled with rootless and excluded people: immigrants, traders, slaves.
The Christian message offered guidelines for living in this strange new world, she says.
"Its universal message, its proclamation of equality, unconditional love, offered everyone in the Roman Empire a new family, a new community, and a way to live," O'Grady says.
Roman rulers eventually found reasons to support the church, she says.
The Christian message of obeying earthly masters -- "Render unto Caesar what is Caesar's and unto God what is God's" -- reduced the potential for social unrest, O'Grady says.
"Christianity told the poor and lowly that their status was noble and that there would be recompense in the afterlife," O'Grady says. "It was a wonderful recipe for creating good, obedient Roman subjects."
A turning point for the early church was the conversion of Constantine. Scholars still debate Constantine's motive. By that time the empire was rife with division, and Christians had become a major political bloc with members in the highest reaches of Roman society, says Stark, the sociologist.
"Constantine was interested so much in church affairs for the rest of his life, but I don't think there's a reason to not think he was a sincere Christian," Stark says. "But he was also an egomaniac and an emperor."
The growth of Christianity was too complex to be attributed to any one factor -- whether it be Constantine, persecution or Christianity's message of compassion and inclusion, Stark says.
"I don't think there was a primary reason," he says. "It was a collection of things. It was all part of a package."
Wrapped in that package, though, were the persecution stories of people such as Perpetua.