Final answer:
Christianity spread from a few communities to nearly the entire Roman Empire and beyond over several centuries, from the first through the sixth centuries, including times of persecution and eventual state tolerance and endorsement.
Step-by-step explanation:
According to the map, it took several centuries for Christianity to spread from a few communities scattered throughout the Roman Empire to (almost) the entire empire and beyond. This large-scale spread and establishment of Christianity occurred from the first through the sixth centuries. This period includes its emergence as a distinct religion in the latter half of the first century, the official toleration under Emperor Constantine in the early fourth century, and later, the declaration as the state religion by Emperor Theodosius towards the end of the fourth century.
Despite initial persecution, including the intense efforts under Emperors such as Nero and Diocletian to suppress the Christian faith, it continued to grow and gain followers. It spread throughout the Mediterranean and North Africa, finding a stronghold in Alexandria, which became a major center for Christian doctrine. The eventual acceptance of Christianity by Roman emperors fundamentally altered Roman society, uniting the Empire under monotheism and setting the foundation for the Byzantine Empire's Christian government.