The standing army of the Empire seems to have been singularly small, little more, indeed, than what was requisite for police duties at home and in the provinces. It was therefore necessary, when any great expedition was contemplated, to call for levies from the subject races. There were several reasons for this peculiar policy in military matters. It was manifestly an economy in time of peace. It made it unnecessary to entrust large bodies of troops, save under exceptional circumstances, to commanders in the remote provinces. The levy system was also an effective one when dealing with such enemies, within and without, as the Empire would have to meet in Asia, and this had been satisfactorily proved in many years of campaigning. It never really failed until brought face to face with an infinitely better armed foe, the Greek of Europe. In the present instance, the force collected is reported by tradition to have amounted to seven hundred thousand men.[5] Here let it be said, as will frequently have to be said in the course of the history of these wars, that the numbers which the Greeks attributed to the Persian armies in various campaigns are, without doubt, invariably exaggerated. There is no fixed ratio in the exaggeration. Sometimes it is manifold; sometimes it is not. The real meaning of the Greek estimate of numbers is that the forces which Persia could put into the field when occasion demanded were of infinitely greater magnitude than any of which the Greek had experience. Even the myriad stood with him for a countless number. In the present instance the force must indeed have been a large one, for the undertaking was great; and the Persian, unless he is much misrepresented in history, preferred on all occasions to have a large numerical margin of safety. Possibly he thought Ahura-mazda was “on the side of the big battalions.” ◆H. iv. 87.◆ The crossing into Europe was affected by throwing a bridge over the Bosphorus in the neighbourhood of Kalchedon.[6] #THE ADVANCE TO THE ISTER.# ◆H. iv. 89.◆ After crossing into Europe, Darius commanded the Ionians, Æolians, and Hellospontines, who conducted the fleet, to sail to the Ister, and while waiting for him there, to build a bridge over the river. They went two days’ sail up the stream, and constructed one at or near the head of the Delta.[7] The first point indicated in the route taken by the army is the source or sources of the Tearos. This was a subtributary of the Agrianes (the modern Ergene), which was itself a tributary of the Hebrus.[8] The Arteskos river, which is the next point mentioned, is not capable of certain identification at the present day. ◆H. iv. 93.◆