The two empires were part of an international trade network that extended from the eastern Mediterranean to the western Pacific. Trade between the great Asian empires and the ensuing movement of peoples resulted in artistic, literary, medical and technological exchanges, along with the diffusion of religious and philosophical ideas.
Chinese prisoners from the Talas river battle, for example, were to have a profound effect on core Arab industries. Chinese paper-makers were settled in Samarkand. In the 13th century Arabs were teaching the art to Spanish and Italians and, until 1911, European historians asserted that paper- making was an eighth-century Arab invention.
This Asian world order was not dominated by any one power. By the eighth century China was only first among equals, and not even this militarily. Her uneasy relationship with powerful neighbours was revealed only four years after the Talas river battle when China was plunged into civil war by General Rokhshan's rebellion.
Rokhshan was of Turkic and Sogdian parentage, appointed in a deliberate Chinese policy. "If we use foreign generals," advised a Chief Minister, "then their ambitions will only be military and not political." Rokhshan showed the weakness of this argument. He won the affections of both the emperor and, most importantly, the emperor's favourite - and young - concubine, Lady Yang. (One of Rokhshan's first gifts to the emperor had been a supply of aphrodisiac pills.)
Assigned to the border hundreds of miles from the capital, he was supplied with luxuries by Lady Yang who appropriated the services of the fast white camels reserved for military crises. But the Chief Minister was not so enamoured of the general's charms and, realising his vulnerability, Rokhshan rebelled in 755.
The rebellion took 11 dreadful and bloody years to quell and victory was only effected with the help of foreign forces, most notably the Turkic Uighurs whose newly acquired empire covered present-day Mongolia. For compensation, they demanded the establishment of horse markets along the Chinese-Uighur border. Over the next century the Chinese empire was obliged to purchase tens of thousands of Uighur horses at an exorbitant rate as the price for peace - in one year, the cost exceeded the annual income of China. Even this was not enough: the Chinese defaulted on payment but could not refuse to send five imperial princesses as brides for successive Uighur kaghans.
The Tibetans, the fourth powerful empire in the region, received only imperial cousins masquerading as princesses, but they also proved fierce opponents and regularly defeated the Chinese forces. One region, nominally under Chinese control, was nicknamed "the Tibetan grain fields" because of the frequency and success of Tibetan raids. Ironically, it was two of the foreign generals appointed by China - a Korean and another Sogdian - who started to turn the tide of military success in China's favour in the 750s, but with Rokhshan's rebellion China withdraw her forces and Tibet took control.
A century later the Tibetan and Uighur empires had both collapsed. The Uighurs moved south to the Silk Road and the area was only re-colonised by China late in the imperial age and thus is still known as "the new territories" - Xinjiang. Central authority in Tibet was re-established after several centuries and it remained a powerful regional force.
Today it is easy to forget that these peoples' current struggle with China for autonomy and territory has a long history and that China was not always so dominant.
Susan Whitfield is the author of `Life Along the Silk Road' (John Murray, pounds 19.99)