There are indications that at an early period a chief or king might offer up a sacrifice, but when the profession of the Brahman became hereditary, no rite could be performed unless presided over by holy men. A sacrifice might be rendered futile by an error in the construction of an altar, or in the order of ceremonial practices, or by failure to select appropriate chants. The Asuras and Rakshasas and other demons were ever hovering round the altar, endeavouring to obstruct ceremonies and to take advantage of ritualistic errors to intercept offerings intended for the gods. It was by making sacrifices that man was believed to obtain power over the gods, or magical control over the forces of nature. [Illustration: GROUP OF PRESENT-DAY BRAHMANS 15 Photo. Frith] For the performance of some sacrifices a day of preparation might be required. Altars had to be erected with mathematical exactness; the stones were blessed and anointed; offerings were made at every stage of the work so that the various deities might give protection in their various spheres. The following extract from one of the Brahmanas affords a glimpse of the preparatory rites:— Thrice he (the priest) perambulates it (the altar); for thrice he walks round it (whilst sprinkling); thus as many times as he walks round it, so many times does he perambulate it.... Having thereupon put that stone into the water pitcher, (he) throws it in that (south-westerly) direction, for that is Nirriti's region; he thus consigns pain to Nirriti's region.... Outside the fire altars he throws it, &c.[130] [130] _Satapatha Brahmana_, trans. by Prof. Eggeling (_Sacred Books of the East_, No. XLIII, p. 170).