Two parts of Europe came under Arab rule: Spain and Sicily. Spain was the last of the large territories to be conquered during the initial Arab conquests, and Sicily was eventually conquered during the Abbasid period. In both areas, the rulers, Arab and North African immigrants, and new converts to Islam lived alongside those who remained Christian or Jewish. During the Abbasid period in particular, Spain and Sicily were important as bridges between the Islamic and Christian worlds, where all faiths and peoples were tolerated. The city of Cordoba in Spain was a glorious metropolis, larger and more prosperous than any in Europe and any but Baghdad in the Arab world itself - it had a population of 100,000, paved streets, street lamps, and even indoor plumbing in the houses of the wealthy. All of the Arabic learning noted above made its way to Europe primarily through contact between people in Spain and Sicily.
The greatest period of contrast between the eastern lands of Byzantium and the caliphates, on the one hand, and most of Europe, on the other, was between the eighth and eleventh centuries. During that period, there were no cities in Europe with populations of over 15,000. The goods produced there, not to mention the quality of scholarship, were of abysmal quality compared to their Arab (or Byzantine) equivalents, and Christian Europe thus imported numerous goods from the Arab world, often through Spain and Sicily. Europe was largely a barter economy while the Muslim world was a currency-based market economy, with Shariah law providing a sophisticated legal framework for business transactions. Especially as Byzantium declined, the Muslim kingdoms stood at the forefront of scholarship, commerce, and military power.