Rein hook

It is designed to hold the reins in place when the driver is away, or his hands are used for something else than driving.

"Narrow-back rein holders" were probably hung to the rider's waist.

They worked as rein hooks, attached at the belt, for horse control.

[3] They may also have been attached at the belt of the charioter for hands-free control.

[5][6] Rein holders were probably introduced in China circa 1200 BCE, where they first appear at Yinxu, from the Northern Zones, where earlier rein holders are known as far as the Minusinsk basin.