From Under the Influence: How Christianity Transformed Civilization by Dr. Alvin Schmidt:
When in Rome, do as the Romans do." So goes an old saying. But when the early Christians arrived in Rome from Jerusalem and parts of Asia Minor, they did not do as the pagan Romans did. They defied the entire system of Rome's morality. The low view of human life among the Romans was one of their pagan depravities: "The individual was regarded as of value only if he was a part of the political fabric and able to contribute to its uses, as though it were the end of his being to aggrandize the State."1 Moreover, the pagan gods taught the people no morals, as St. Augustine, a former pagan himself, knew from personal experience (The City of God 2.4). This too did not enhance the value of human life.
The low value of life among the Romans was a shocking affront to the early Christians, who came to Rome with an exalted view of human life. Like their Jewish ancestors, they saw human beings as the crown of God's creation; they believed that man was made in the image of God (Genesis 1:27). Although that image was tarnished by man's fall into sin, they nevertheless believed the words of the psalmist to be true: "You made him [man} a little lower than the heavenly beings and crowned him with glory and honor" (Psalm 8:5). They also knew that God so honored human life that he himself assumed it by becoming incarnate in the person of Jesus Christ, his only begotten Son (John 1:14). Thus, unlike the Romans, Christians did not hold human life to be cheap and expendable. It was to be honored and protected at all costs, regardless of its form or quality. By doing so, they countered many depravities that depreciated human life.
Update: The author released what appears to be a revised or expanded edition, under a new title. Unlike the book linked above, How Christianity Changed the World is still in print: in paperback, ebook, and audio.