Greece has one of the longest histories of any country, and is considered the cradle of Western civilization, and as such, is the birthplace of democracy, Western philosophy, the Olympic Games, Western literature, historiography, political science, major scientific and mathematical principles, and Western drama, including both tragedy and comedy. Greece was first unified under Philip of Macedon in the fourth century BC. His son Alexander the Great rapidly conquered much of the ancient world, spreading Greek culture and science from the eastern Mediterranean to the Indus River. Annexed by Rome in the second century BC, Greece became an integral part of the Roman Empire and its successor, the Byzantine Empire. The first century AD saw the establishment of the Greek Orthodox Church, which shaped the modern Greek identity and transmitted Greek traditions to the wider Orthodox World. Falling under Ottoman dominion in the mid-15th century, the modern nation state of Greece emerged in 1830 following the war of independence. Greece's rich historical legacy is reflected in large part by its 17 UNESCO World Heritage Sites, among the most in Europe and the world.