his armies out. Darius encountered mockery and taunting from the rebels, including the famous saying "Oh yes, you will capture our city, when mules shall have foals." For a year and a half, Darius and his armies were unable to retake the city, though he attempted many tricks and strategies—even copying that which Cyrus the Great had employed when he captured Babylon. However, the situation changed in Darius's favour when, according to the story, a mule owned by Zopyrus, a high-ranking soldier, foaled. Following this, a plan was hatched for Zopyrus to pretend to be a deserter, enter the Babylonian camp, and gain the trust of the Babylonians. The plan was successful and Darius's army eventually surrounded the city and overcame the rebels. During this revolt, Scythian nomads took advantage of the disorder and chaos and invaded Persia. Darius first finished defeating the rebels in Elam, Assyria, and Babylon and then attacked the Scythian invaders. He pursued the invaders, who led him to a marsh; there he found no known enemies but an enigmatic Scythian tribe. European Scythian campaign The Scythians were a group of north Iranian nomadic tribes, speaking an Eastern Iranian language (Scythian languages) who had invaded Media, killed Cyrus in battle, revolted against Darius and threatened to disrupt trade between Central Asia and the shores of the Black Sea as they lived between the Danube River, River Don and the Black Sea. Darius crossed the Black Sea at the Bosphorus Straits using a bridge of boats. Darius conquered large portions of Eastern Europe, even crossing the Danube to wage war on the Scythians. Darius invaded European Scythia in 513 BC, where the Scythians evaded Darius's army, using feints and retreating eastwards while laying waste to the countryside, by blocking wells, intercepting convoys, destroying pastures and continuous skirmishes against Darius's army. Seeking to fight with the Scythians, Darius's army chased the Scythian army deep into Scythian lands, where there were no cities to conquer and no supplies to forage. In frustration Darius sent a letter to the Scythian ruler Idanthyrsus to fight or surrender. The ruler replied that he would not stand and fight with Darius until they found the graves of their fathers and tried to destroy them. Until then, they would continue their strategy as they had no cities or cultivated lands to lose. Despite the evading tactics of the Scythians, Darius' campaign was so far