Śatapatha Brāhmaṇa ("of a hundred paths") 14.1.2.16

14.1.2.16

pariśritam bhavati etadvai devā abibhayuryadvai na imamiha rakṣāṃsi nāṣṭrā na hanyuriti tasmā etām puram paryaśrayaṃstathaivāsmā ayametām puram pariṣrayati

It is an enclosed space;--for at that time the gods were afraid, thinking, 'We hope that the fiends, the Rakshas, will not injure here this our (Pravargya):' they accordingly enclosed for it this stronghold, and in like manner does this (Sacrificer) now enclose for it this stronghold.