When an empire falls it does not disappear in a puff of smoke. A new empire does not appear immediately to occupy its space. The geopolitical structure of the empire that falls is usually the first to go, then go the dominant institutions of its domestic political structure, but the cultural, religious, and financial institutions, and some of the political institutions get reinterpreted and transmitted in several ways and remain in existence for centuries. The Persian Empire fell in the fourth century BC, but its cultural and linguistic legacy can still be detected in the Middle East, the Indian Subcontinent, and Europe. The Western Roman Empire fell in the fifth century AD and the Eastern Roman Empire fell in the fifteenth century AD but their political and cultural institutions still exist in Europe, Asia, North Africa and North America.