Śatapatha Brāhmaṇa ("of a hundred paths") 3.6.2.21

3.6.2.21

te vā ete | somasyaiva guptyai nyupyanta āhavanīyaḥ purastānmārjālīyo dakṣiṇata āgnīdhrīya uttarato 'tha ye sadasi te paścāt

Now it is for the protection of Soma that those (hearths) are thrown up, to wit the Âhavanîya in front (on the high altar), the Mârgâlîya in the south, and the Âgnîdhrîya in the north; and those that are in the Sadas (protect him) from behind.