at its maximum extent, tang expansion brought china into direct contact with the rising umayyad caliphate. china's western borders reached the eastern frontier of the caliphate. following the arab defeat of sassanid persia in 651, the caliphate began its expansion into central asia, competing with the tang's sphere of influence in the region. chinese and islamic troops finally clashed at the battle of aksu in 717 and the battle of talas in 751. though victorious in 717, the chinese lost against the arabs, now under abbasid rule, and the arab army captured chinese papermaking craftsmen. an arabic record of the conflict claims that the battle led to the introduction of papermaking to the islamic world.