16. First great expedition of Darius undertaken against the Scythians inhabiting the lands north of the Black sea: the former irruption of the Scythians into Asia afforded a pretext for the war, which, therefore, was considered as a general national undertaking. Unsuccessful as the Persian arms were in this vast expedition against the Scythians, and disgraceful as was the retreat from the barren steppes of the Ukrain, yet the power of Darius was established in Thrace and Macedonia, and the Persians obtained firm footing in Europe. Concerning the peculiar character of the Persian national wars, or great campaigns, in which all the conquered nations were obliged to participate, contrasted with the other wars waged by Persian troops alone. 17. The next expedition made by Darius was more successful. It was carried on along the banks of the Indus, down which river Scylax, a Greek, had previously sailed on a voyage of discovery. The highlands north of the Indus were then subjected to the Persian dominion, and the Indus became the boundary of the kingdom. About the same time that Darius was engaged on the Danube and the Indus, Aryandes, his viceroy in Egypt, led an expedition against Barca, to avenge the murder of king Arcesilaus; a war which terminated in the destruction of the city, and the transplantation of its inhabitants into Asia. 18. However trifling the first occurrence which gave rise to the revolt of the Asiatic Greeks, it was much more important in its consequences. It was set on foot by Aristagoras, lieutenant-governor of Miletus, who was secretly supported by his relation, the offended Histiaeus, then resident at the Persian court. The share taken by the Athenians in this rebellion, which led to the burning of Sardes, was the origin of the national hatred between Persia and European Greece, and of the long series of wars that ensued. The confederates were this time defeated; but the naval battle off the island of Lada, could hardly have had such a fatal result, had not the league been previously corrupted by the craft and gold of Persia. Be that as it may, this war ended in the reduction of the Ionians, and the destruction of Miletus, their flourishing capital; a city which in those days, together with Tyre and Carthage, engrossed the trade of the world.