Final answer:
By the end of the 4th century, about 10% of the Roman population was Christian during the Great Persecution of 303.
Step-by-step explanation:
During the Great Persecution of 303, it is difficult to determine the exact portion of the Roman population that was Christian. However, by the early 4th century, Christianity had gained significant followers and was spreading across the Roman Empire. The official persecution of Christians by Diocletian indicates that Christianity had already become a sizable and influential religious group at the time. It is estimated that by the end of the 4th century, about 10% of the Roman population was Christian.