dependence as analogous to a civil contract between man and god. Both
sides are under obligation to fulfil their part: if a god answers a
man's prayer, he must be repaid by a thank-offering: if the man has
fulfilled 'his bounden duty and service,' the god must make his return:
if he does not, either the cause lies in an unconscious failure on the
human side to carry out the exact letter of the law, or else, if the
god has really broken his contract, he has, as it were, put himself out
of court and the man may seek aid elsewhere. In this notion we have the
secret of Rome's readiness under stress of circumstances, when all
appeals to the old gods have failed, to adopt foreign deities and cults
in the hope of a greater measure of success.

The contract-notion may perhaps appear more clearly if we consider one
or two of the normal religious acts of the Roman individual or state.
Take first of all the performance of the regular sacrifices or acts of
worship ordained by the state-calendar or the celebration of the
household _sacra_. The _pietas_ of man consists in their due
fulfilment, but he may through negligence omit them or make a mistake
in the ritual to be employed. In that case the gods, as it were, have
the upper hand in the contract and are not obliged to fulfil their
share, but the man can set himself right again by the offering of a
_piaculum_, which may take the form either of an additional sacrifice
or a repetition of the original rite. So, for instance, when Cato is
giving his farmer directions for the lustration of his fields, he
supplies him at the end with two significant formulæ: 'if,' he says,
'you have failed in any respect with regard to all your offerings, use
this formula: "Father Mars, if thou hast not found satisfaction in my
former offering of pig, sheep, and ox (the most solemn combination in
rustic sacrifices), then let this offering of pig and sheep and ox
appease thee": but if you have made a mistake in one or two only of