Cyrus, on his part, allowed the Lydians to retire unmolested, thus confirming his adversary in the mistaken estimate which he had formed of Persian courage and daring. Anticipating the course which Croesus would adopt under the circumstances, he kept his army well in hand, and, as soon as the Lydians were clean gone, he crossed the Halys, and marched straight upon Sardis. Croesus, deeming himself safe from molestation, had no sooner reached his capital than he had dismissed the bulk of his troops to their homes for the winter, merely giving them orders to return in the spring, when he hoped to have received auxiliaries from Sparta, Babylon, and Egypt. Left thus almost without defence, he suddenly heard that his audacious foe had followed on his steps, had ventured into the heart of his dominions, and was but a short distance from the capital. In this crisis he showed a spirit well worthy of admiration. Putting himself at the head of such an army of native Lydians as he could collect at a few hours’ notice, he met the advancing foe in the rich plain a little to the east of Sardis, and gave him battle immediately. It is possible that even under these disadvantageous circumstances he might in fair fight have been victorious, for the Lydian cavalry were at this time excellent, and decidedly superior to the Persian. But Cyrus, aware of their merits, had recourse to stratagem, and by forming his camels in front, so frightened the Lydian horses that they fled from the field. The riders dismounted and fought on foot, but their gallantry was unavailing. After a prolonged and bloody combat the Lydian army was defeated, and forced to take refuge behind the walls of the capital.
Croesus now in hot haste sent off fresh messengers to his allies, begging them to come at once to his assistance. He had still a good hope of maintaining himself till their arrival, for his city was defended by walls, and was regarded by the natives as impregnable. An attempt to storm the defences failed; and the siege must have been turned into a blockade but for an accidental discovery. A Persian soldier had approached to reconnoitre the citadel on the side where it was strongest by nature, and therefore guarded with least care, when he observed one of the garrison descend the rock after his helmet, which had fallen from his head, pick it up, and return with it. Being an expert climber, he attempted the track thus pointed out to him, and succeeded in reaching the summit. Several of his comrades followed in his steps; the citadel was surprised, and the town taken and plundered.