The unreliability and vagueness of the story of the campaign have led to the formation in modern times of many conjectures as to the object with which it was undertaken.
It has been represented as an attempt to make the Euxine a Persian lake. Such a theory must assume that Darius carried his operations far beyond the Ister. On this point sufficient has been said. But apart from this the theory is met by two other difficulties. What object could be gained by success in so bald a design? And if such a design existed, why was the fleet left at the Ister?
Again, it has been ascribed to mere lust of conquest. That is, indeed, not an uncommon characteristic with Eastern rulers. But Darius was not an Eastern ruler of the ordinary type. His wars, in so far as their history is known, are not waged from mere irrational land-hunger, but in obedience to rational policy, whose main lines are even now distinguishable. That he intended in this campaign to conquer something is obvious. But did he intend to make conquests in Scythia? Had he, too, no other conceivable motive than mere land-hunger behind the intention of conquest?
A more attractive theory which has been put forward in explanation of the object of the expedition is that, in accordance with his commercial policy, he attempted to open up, possibly to acquire, the rich region north of the Euxine. In that case it would certainly have been expected that he would have made one of the Greek harbours on the north coast of that sea the base of his operations, and have transferred his fleet thither. He could have got plenty of information on the subject from his Asiatic Greek vassals.
A theory which has been recently put forward is that his real object was to get hold of that gold region in the land of the Agathyrsi, a tribe mentioned in Herodotus’ account of the campaign. THE INTENT OF THE CAMPAIGN. This gold-bearing region must be identified with that on the western border of the modern province of Transylvania, which was included in the Roman province of Dacia. It is, however, impossible to say that there is even presumptive evidence of such an intention on Darius’ part.
It must be confessed that the evidence is not of such a nature that any theory as to the object of the campaign can be put forward with confidence. There are, however, two questions which must be taken into account in any theory on the subject which is to have the merit of plausibility:—
(1) What were the net results of the campaign?
(2) Did the acts of Darius in any way declare his intentions?
The net results of the campaign were the submission of the Thracian tribes on the Euxine coast south of Hæmus, and the conquest and apparent submission of the Getæ between Hæmus and the Ister.
The intention of Darius to cross the Ister existed apparently from the beginning of the campaign. He sent the fleet thither with orders to prepare a bridge; but the intention not to proceed far beyond that river is almost equally clearly shown by his leaving his fleet at the point of crossing. Whether this second intention was part of the original design is another question. The tale of the countermanding of the orders given to the Greeks at the river, absurd though it is, may rest on a remote foundation of fact; and the fact may have been that Darius did actually modify his original plans on his arrival at the Ister.