The contrast between the civilizations of Eurasia is best illustrated in their capital cities.
The Frankish Empire had an insignificant town as its capital - Aix-la-Chapelle with hardly
more than 2-3000 inhabitants.
Cordoba - the capital of Omayyad Spain - contained a famous library, 471 mosques, 80'000 shops and housed about half a million people.
Constantinople with a quarter of a million people was, next to Cordoba, the greatest city of Europe, including Rome which at that time was in full decline.
The capital of the Abbasid caliphs - Baghdad - founded in 762 by al-Mansur, who employed 100'000 men on the building of the circular city with a diameter of 2'600 meters, was almost immediately too small for the growing population. By 814 it covered an area of 10 x 9 km, the equivalent of modern Paris within the outer boulevards.
But the outstanding city of Eurasia was Ch'ang-an, capital of Tang China. The city measured 9.4 x 8.4 km with 14 east-west boulevards and several north-south avenues the main avenue leading from the imperial palace to the south gate over 150 meters wide. The city had 90 Budhhist and 16 Taoist places of worship, four Zoroastrian temples and two Nestorian Christian churches. It housed about a million people within its walls and probably another million in the suburbs outside.
So impressive was the Chinese metropolis that the rulers of Japan used it as a model for their capital at Kyoto.