Śatapatha Brāhmaṇa ("of a hundred paths") 13.1.6.3

13.1.6.3

rāṣṭraṃ vā aśvamedhaḥ rāṣṭra ete vyāyacante ye'śvaṃ rakṣanti teṣāṃ ya udṛcaṃ gacanti rāṣṭreṇaiva te rāṣṭram bhavantyatha ye nodṛcaṃ gacanti rāṣṭrātte vyavacidyante tasmādrāṣṭryaśvamedhena yajeta parā vā eṣa sicyate yo'balo'śvamedhena yajate yadyamitrā aśvaṃ vinderanyajño'sya vicidyeta pāpīyāntsyācataṃ kavacino rakṣanti yajñasya saṃtatyā avyavacedāya na pāpīyānbhavatyathānyamānīya prokṣeyuḥ saiva tatra prāyaścittiḥ

Verily, the Asvamedha means royal sway: it is after royal sway that these strive who guard the horse. Those of them who reach the end become (sharers in) the royal sway, but those who do not reach the end are cut off from royal sway. Wherefore let him who holds royal sway perform the horse-sacrifice; for, verily, whosoever performs the horse-sacrifice, without possessing power, is poured (swept) away.--Now, were unfriendly, men to get hold of the horse, his sacrifice would be cut in twain, and he would become the poorer for it. A hundred men clad in armour guard it for the continuity and uninterrupted performance of the sacrifice; and he will not become the poorer for it; (but if it be lost) they should fetch another (horse), and sprinkle it: this is the expiation in that case.