Cato in his treatise on agriculture has left us, in the form of instructions to a real or imaginary bailiff, the formula of the lustratio as it was used in the second century B.C. It is obviously applicable in detail rather to the estate of that period than to a farm of primitive Latium: there are, for example, words which suggest that it was not necessary in those days to go in procession round the whole of the boundary; as was the case afterwards with the lustratio of the ager Romanus, the form survived accommodated to the great increase of the land concerned. But the two main features of the whole rite are no doubt identical with those of the earliest form of it--i. e. the procession of the victims, ox, sheep, and pig, the farmer’s most valuable property, with the sacrificer and his helps, in this case the bailiff and his assistants: and secondly the prayer to Mars pater, after libations to Janus and Jupiter, asking for his kindly protection of the whole _familia_ of the farm, together with the crops of every kind, and the cattle within the boundary-line. Though it is not explicitly told us, we can hardly doubt that originally the procession followed the boundary-line, and thus served to keep it clear in the memory as well as to preserve everything within it from hostile spirits outside of it. In Cato’s formula it is disease, calamity, dearth, and infertility, that the farmer seeks to ward off--that is the language of the second century B.C.: and it is Mars pater who is invoked, i. e. a great god who has long ago emerged from the crowd of impersonal spirits; but we need not doubt that the primitive farmer used language of a different kind, and addressed the spirits of disease and dearth themselves, of whom one survived into historic times--Robigus, the spirit of mildew. In the ritual of the Arval Brethren, who perhaps retained some details more antique than those of Cato’s instructions, it is a nameless deity, the Dea Dia, who is the chief object of petition (_Acta Fratr. Arv._, p. 48).