Before his own day, he says, {197b} the events of the world were unconnected and separate and the histories confined to particular countries.  Now, for the first time the universal empire of the Romans rendered a universal history possible. {198a} This, then, is the august motive of his work:  to trace the gradual rise of this Italian city from the day when the first legion crossed the narrow strait of Messina and landed on the fertile fields of Sicily to the time when Corinth in the East and Carthage in the West fell before the resistless wave of empire and the eagles of Rome passed on the wings of universal victory from Calpe and the Pillars of Hercules to Syria and the Nile.  At the same time he recognised that the scheme of Rome’s empire was worked out under the aegis of God’s will. {198b} For, as one of the Middle Age scribes most truly says, the [Greek] of Polybius is that power which we Christians call God; the second aim, as one may call it, of his history is to point out the rational and human and natural causes which brought this result, distinguishing, as we should say, between God’s mediate and immediate government of the world.

With any direct intervention of God in the normal development of Man, he will have nothing to do:  still less with any idea of chance as a factor in the phenomena of life.  Chance and miracles, he says, are mere expressions for our ignorance of rational causes.  The spirit of rationalism which we recognised in Herodotus as a vague uncertain attitude and which appears in Thucydides as a consistent attitude of mind never argued about or even explained, is by Polybius analysed and formulated as the great instrument of historical research.

Herodotus, while believing on principle in the supernatural, yet was sceptical at times.  Thucydides simply ignored the supernatural.  He did not discuss it, but he annihilated it by explaining history without it.  Polybius enters at length into the whole question and explains its origin and the method of treating it.  Herodotus would have believed in Scipio’s dream.  Thucydides would have ignored it entirely.  Polybius explains it.  He is the culmination of the rational progression of Dialectic.  ‘Nothing,’ he says, ’shows a foolish mind more than the attempt to account for any phenomena on the principle of chance or supernatural intervention.  History is a search for rational causes, and there is nothing in the world—­even those phenomena which seem to us the most remote from law and improbable—­which is not the logical and inevitable result of certain rational antecedents.’

Some things, of course, are to be rejected a priori without entering into the subject:  ‘As regards such miracles,’ he says, {199} ’as that on a certain statue of Artemis rain or snow never falls though the statue stands in the open air, or that those who enter God’s shrine in Arcadia lose their natural shadows, I cannot really be expected to argue upon the subject.  For these things are not only utterly improbable but absolutely impossible.’