During the medieval era the Eastern Orthodox Church was centered in the Byzantine Empire. The Patriarch of Constantinople was considered the leader of Eastern Orthodoxy. Constantinople was the capital of the Byzantine Empire.

Pope Gregory I served as Pope from 590 C.E. to 604 C.E. He is one of the most significant and revered Popes in the history of the Catholic Church. His writings, of which there were many, continue to be influential to this day. He is considered by most scholars to be the founder of the medieval Papacy and the man who ensured the continued power of the Pope, by transferring his spiritual authority into a more secular role. He was the first Pope to take an active role in the political life of Europe and laid the foundations for the behavior of countless Popes that followed.

The Great Schism of Christianity, sometimes called the East-West Schism, took place in 1054 C.E. It involved the fracture of Christianity between the Catholic and Eastern Orthodox churches. The dispute arose over different interpretations of scripture between two of the major centers of Christian theology - the Vatican and Constantinople. After the Great Schism Catholicism continued to be centered in Vatican City and Eastern Orthodoxy was centered in Constantinople.

The early Christian "apologetics" were theologians who were primarily concerned with proving the veracity of the Christian faith and defending Christian truth from outside attacks. Many of the earliest works of Christian theology fall under the category of "apologetics." Paul the Apostle and Augustine of Hippo are two famous examples of Christian "apologetics."

When Islamic armies conquered Spain during the eighth century, they gave more legal rights to the Jewish population of their new kingdoms. Conquering almost all of the Iberian Peninsula within one hundred years, giving Jews positions of influence and power as advisors and tradesmen. When Christians fully retook the Peninsula in 1492, the Christian Monarchs Ferdinand and Isabella began the Inquisition, which either forced the Jews to convert to Catholicism or flee the country.

The Prophet Muhammad died in 632, having united the entire Arabian peninsula into a single polity under Islam. By 732, Islamic armies had swept across north Africa, conquered the Iberian Peninsula, and were heading into France. At the Battle of Tours, a Christian army under Charles Martel defeated the Islamic army of Abdul Rahman, halting the Islamic advance and making the Muslim armies stop in Spain.

The primary sacred religious text of Islam is called the Quran. The Bible is the primary sacred religious text of Christianity; the Torah the primary sacred religious text of Judaism; and the Vedas the primary sacred religious texts of Hinduism. The Gospels are a part of the Christian New Testament of the Bible that tells of Jesus Christ from various perspectives (most importantly Matthew's, Mark's, Luke's, and John's).

The prophet Muhammad is considered by Muslims to be the last prophet sent by God to mankind in order to restore the true monotheistic religion of Abraham. He unified the region of Arabia under one religion, Islam, and paved the way for the subsequent fifteen hundred years of Islamic history. In the early years of his preaching, Muhammad was mostly condemned by the authorities in Mecca, so he and his followers fled to Medina, where he continued to teach and preach for eight years until he had gained a large enough following to march on the city of Mecca.