Islam emerged from what is modern day Saudi Arabia in the 7th century, and never looked back. Muslim armies swept across North Africa and invaded Catholic Spain, destroying or converting the Christian communities along the way. They turned churches into mosques, and made Islam the official religion. Muslim armies also took over the Holy Land, destroyed the last non-Islamic Persian empire, and moved into Asia Minor (modern day Turkey). By the 16th century, Islam had destroyed the Christian Byzantine Empire, had taken over Constantinople, and had turned the Hagia Sophia — the most beautiful church in Christendom — into a mosque. A century later, Muslim armies were outside the gates of Vienna.