The sciences of only one nation, the Greeks, have come down to us, because they were translated through Al-Ma'mun's efforts. He was successful in this direction because he had many translators at his disposal and spent much money in this connection.
Ibn KhaldunAt the beginning of a dynasty, taxation yields a large revenue from small assessments. At the end of the dynasty, taxation yields a small revenue from large assessments.
Ibn Khaldun