However, according to Houhanshu (the Book of Later Han, penned by a Chinese historian during the fifth century and considered an authoritative record of the Han history between 25 and 220), about 10, or at least five or six, diplomatic groups were dispatched annually by the Han court to Central Asia during this period to buy horses.

"For the Han people the horses had become a fetish and a cult, as evidenced by their newly assigned name, heavenly horses," says Rong Xinjiang, a professor of history at Peking University and an expert on the Silk Road.

"Compared with the indigenous Chinese breeds, these heavenly horses feature longer and spikier ears that made them look more vigilant. They also had elongated bodies that appeared both athletic and elegant."

One image that best illustrates this kinetic elegance is a bronze horse unearthed in Gansu province, Northwest China, across which the ancient Silk Road wound. With mouth open, ears pricked and nostrils flared, the steed charges ahead at full tilt. Its wind-whipped mane conveys momentum, but what really captures its speed and renders this sculpture an iconic work of art is a sparrow that appears under one hind hoof of the horse. It is as if the galloping horse, in a fleeting moment as it overtakes the low-flying sparrow, is stamping on the bird's wings.

The horse, coated in green patina, turned up in the tomb of a Han general, with a whole legion comprised of lance-holding horsemen and horse-drawn chariots. In most cases the mane on the horses' forehead is portrayed as being tied high up and blown back by strong wind. Another distinct feature is the tail, raised to form one curve or two. It is as if a powerful life force has charged through the horse, head to hind, and reached its endpoint undiminished.