Stirrups first appeared in India around 500BCE. They were widespread by 500CE. The mongols were 1200CE. You may be thinking of the Huns. Incidentally, it is

Stirrups first appeared in India around 500BCE. They were widespread by 500CE. The mongols were 1200CE. You may be thinking of the Huns. Incidentally, it is remarkable that it took 1000 years for the stirrup to spread across eurasia. I have no good explanation for this.