While Bābur was now in Qūndūz his sister Khān-zāda arrived there, safe-returned under escort of the Shāh's troops, after the death in the battle of Merv of her successive husbands Shaibānī and Sayyid Hādī, and with her came an envoy from Ismā`īl proffering friendship, civilities calculated to arouse a hope of Persian help in Bābur. To acknowledge his courtesies, Bābur sent Mīrzā Khān with thanks and gifts; Ḥaidar says that the Mīrzā also conveyed protestations of good faith and a request for military assistance. He was well received and his request for help was granted; that it was granted under hard conditions then stated later occurrences shew. 917 AH.-MARCH 31ST 1511 TO MARCH 19TH 1512 AD. _a. Second attempt on Ḥiṣār._ In this year Bābur moved again on Ḥiṣār. He took post, where once his forbear Tīmūr had wrought out success against great odds, at the Pul-i-sangīn (Stone-bridge) on the Sūrkh-āb, and lay there a month awaiting reinforcement. The Aūzbeg sulṯāns faced him on the other side of the river, they too, presumably, awaiting reinforcement. They moved when they felt themselves strong enough to attack, whether by addition to their own numbers, whether by learning that Bābur had not largely increased his own. Concerning the second alternative it is open to surmise that he hoped for larger reinforcement than he obtained; he appears to have left Qūndūz before the return of Mīrzā Khān from his embassy to Ismā`īl, to have expected Persian reinforcement with the Mīrzā, and at Pul-i-sangīn, where the Mīrzā joined him in time to fight, to have been strengthened by the Mīrzā's own following, and few, if any, foreign auxiliaries. These surmises are supported by what Khwānd-amīr relates of the conditions [specified later] on which the Shāh's main contingent was despatched and by his shewing that it did not start until after the Shāh had had news of the battle at Pul-i-sangīn. At the end of the month of waiting, the Aūzbegs one morning swam the Sūrkh-āb below the bridge; in the afternoon of the same day, Bābur retired to better ground amongst the mountain fastnesses of a local Āb-dara. In the desperate encounter which followed the Aūzbegs were utterly routed with great loss in men; they were pursued to Darband-i-ahanīn (Iron-gate) on the Ḥiṣār border, on their way to join a great force assembled at Qarshī under Kūchūm Khān, Shaibānī's successor as Aūzbeg Khāqān. The battle is admirably described by Ḥaidar, who was then a boy of 12 with keen eye watching his own first fight, and that fight with foes who had made him the last male survivor of his line. In the evening of the victory Mahdī, Ḥamza and Ḥamza's son Mamak were brought before Bābur who, says Ḥaidar, did to them what they had done to the Mughūl Khāqāns and Chaghatāī Sulṯāns, that is, he retaliated in blood for the blood of many kinsmen. _b. Persian reinforcement._