The dinar, derived from the Roman denarius aureus, is the name for the gold currency of the Islamic coinage system. In the conquered territories the Islamic conquerors had at first copied the Byzantine coins in circulation there. In his coinage reform, Caliph Abd al Malik also pushed through the Koran's prohibition of pictures for gold coins. Since then the important religious tenets of the Koran, elaborated more or less artistically, have been a feature of the Islamic gold coins: "There is no God but Allah" and "Muhammad is his prophet".
This gold dinar was minted under the Abbasid Caliph al-Ma'Mun (813-833), who carried out a coinage reform which remained valid for centuries. The Islamic gold coins became the most important gold currency in the world in the early and high Middle Ages. The dinar constituted a counter-currency to the Byzantine solidus and adopted its weight of 4.25 g. It was widespread on the coasts of the western Mediterranean. The quarter dinar (2.3 g) was imitated in Sicily and southern Italy by the Normans as the tari. Just as the Celts copied the Greek and Roman coins earlier on, so Christian rulers in Spain, Sicily and Jerusalem imitated the Arab coins: a good example of cultural exchange on the level of coinage.