These exact formulae of invocation and sacrifice were really the outward expression of a fear of the unknown, and its power to hinder and injure man; for the old Roman did not know his gods intimately, inasmuch as they took no human shape, and did not dwell in buildings made by hands. We have illustrated this ignorance of his again and again, and the vagueness and fluidity of the religious conceptions of the Roman mind. The remedy for this weakness was found, as with the Jews, in a remarkable formularity of ritual, both as regards time, place, and method of worship: in a series of elaborate prescriptions drawn up by experts, going even so far as to anticipate the consequence of an unintentional omission or error by piacular acts. This in time, and under State organization, became a science, and finds its parallel in the science of legal formulae. But there was a difference between the two sciences, even for the Roman. In religious acts, the human mind is dealing with the unseen and unknown, not with human beings who can be calculated with or outwitted. His fear of the unknown was thus for the primitive Roman a wholesome discipline; and his attitude towards it he aptly and characteristically called _religio_, because it _bound_ him to the performance of certain regulated duties, calculated to keep his footsteps straight as he walked daily in this unseen world: duties which even in the family and clan must have been to some extent systematized, and which when the city-state was reached took the definite form of a calendar of public prayers, sacrifices, and festivities.