"By the time of the Katha Upanishad, the metaphor of the horse (and the chariot, to which we will turn shortly), though slightly altered from the `Rgvedic imagery, had become perfectly explicit: “Know the self (åtman) to be the chariot’s master, and the body, the chariot itself; know the intellect (buddhi) to be the charioteer, and the mind (manas), the reins” (1.3.3); the horses, the Upanishad continues, are the five senses (indriya-s) which must be reined in by our intellect and (higher) mind, and ultimately the self. The chariot, here, stands for the body or our external being."