The history of Russia is often considered as if that immense country had always been an isolated continent. However, at the time of its rise as a nation, it was politically a province of the Mongol Empire, whose capital was in Central Asia; and ecclesiastically, it was a dependency of the Orthodox Patriarchate of Constantinople, or Byzantium. This book describes the role of Byzantine (predominantly ecclesiastical) diplomacy in the emergence of Moscow as the capital of Russia in the fourteenth century, and the cultural, religious and political ties which connected the Northern periphery of the Byzantine Orthodox 'Commonwealth' with its centre in Constantinople. After 1370, the religious and monastic revival in Byzantium and the weakening of Mongol power provided an orientation to the policies of the Orthodox church in Russia: towards supra-national unity, spiritual and artistic achievements, and political reconciliation between principalities.