Three characteristics of the Roman Empire are typically credited with aiding the advancement of Christianity. First, the Pax Romana, or Roman peace, created a relatively stable political climate that allowed for travel in the years immediately before the birth of Christ until about 200 AD. Since the territory of the Mediterranean Sea was not ravaged by wars, everyday Christians, as well as missionaries, could travel throughout the kingdom freely, bearing the good news of Christ. The Romans had a hands-off policy toward local religions in their provinces and allowed local governance as long as citizens paid taxes and allowed military occupation. More than once, early Christian leaders were protected from harm by Roman laws and rulers.
Second, Roman roads made travel much easier than it had ever been. Although the roads were built to allow Roman armies quick access to the regions under their control, they were also used for commerce and personal travel. Previously, sections of the Mediterranean region would become impassable in the rainy season. Roman-engineered roads were of such high quality that many are still used today. This network of highways allowed missionaries to easily make their way around the Roman Empire.
Finally, a common language greatly enhanced the spread of Christianity. Koine Greek had become the commonly spoken language in the region of the Mediterranean. This enabled missionaries like Paul to go to far-off lands and still be understood. The Bible refers to Jesus coming "in the fullness of time." Indeed, the convergence of several characteristics within the Roman Empire—including Roman laws, Roman roads, and a common language—created an environment especially conducive to sharing the gospel widely and rapidly.