Constantinople was a prime hub in a trading network that at various times extended across nearly all of Eurasia and North Africa. Some scholars argue that, up until the arrival of the Arabs in the 7th century, the Empire had the most powerful economy in the world. The Arab conquests, however, would represent a substantial reversal of fortunes contributing to a period of decline and stagnation. Constantine V's reforms (c. 765) marked the beginning of a revival that continued until 1204. From the 10th century until the end of the 12th, the Byzantine Empire projected an image of luxury, and the travelers were impressed by the wealth accumulated in the capital. All this changed with the arrival of the Fourth Crusade, which was an economic catastrophe. The Palaiologoi tried to revive the economy, but the late Byzantine state would not gain full control of either the foreign or domestic economic forces.
One of the economic foundations of the empire was trade. The state strictly controlled both the internal and the international trade, and retained the monopoly of issuing coinage. Constantinople remained the single most important commercial centre of Europe for much of the Medieval era, which it held until the Republic of Venice slowly began to overtake Byzantine merchants in trade; first through tax exemption under the Komnenoi, then under the Latin Empire.
The Umayyad Caliphate was the second of the four major Islamic caliphates established after the death of Muhammad. It was ruled by the Umayyad dynasty, whose name derives from Umayya ibn Abd Shams, the great-grandfather of the first Umayyad caliph. Although the Umayyad family originally came from the city of Mecca, their capital was Damascus. At its greatest extent, it covered more than five million square miles (13,000,000 km2), making it the largest empire the world had yet seen, and the seventh largest contiguous empire ever to exist. After the Umayyads were overthrown by the Abbasid Caliphate, they fled across North Africa to the Iberian Peninsula (Al-Andalus), where they established the Caliphate of Córdoba, which lasted until 1031 before falling due to the Fitna of al-Ándalus.
The Abbasid dynasty controlled the Muslim caliphate from 750 to 1258. It was the second of the two greatest dynasties, overthrowing the Umayyads to gain control, and destroyed by the invasion of the Mongols. The Abbasids were noted for promoting commerce and encouraging the arts, especially during the reigns of al-Mansur, Harun ar-Rashid, and al-Ma'mun.