attacked Rouran together, but Rouran's Chuluo Khan, Yujiulü Tuhezhen eluded them and did not engage them. In fall 449, however, Tuoba Na was able to inflict heavy losses on Rouran, and for several years Rouran did not attack. In 450, Emperor Taiwu, accusing Liu Song's Emperor Wen of having fostered Gai's rebellion, attacked Liu Song, putting Xuanhu (懸瓠, in modern Zhumadian, Henan) under siege for 42 days but could not capture it, and he withdrew. Later in 450, a major political mystery occurred in Northern Wei—for reasons not completely clear now, Emperor Taiwu had Cui Hao put to death, along with his particular cadet branch of his clan and any other person named Cui from Cui's home commandery of Qinghe (清河, roughly modern Xingtai, Hebei), as well as the cadet branches of several other clans with marital relations to Cui's. The publicly announced reason was that Cui had unduly revealed imperial infamy, when he wrote and published an official history, but what Cui did was never fully stated. The modern historian Bo Yang speculated that Cui had revealed that Emperor Taiwu's grandfather Emperor Daowu had been a traitor, and also that Cui was then in a major political confrontation with Crown Prince Huang, who manufactured part of the charges against Cui. (See here for details.) However, Bo's speculation, while having some evidentiary support, is not close to being conclusively shown, and why Emperor Taiwu suddenly so rashly and so severely punished the man that he had trusted for decades is fairly unclear. (It should be further noted that during the entire incident, Cui was described as being so fearful that he could not speak a single word, which appeared highly inconsistent with Cui's personality and character, suggesting that Cui had himself been poisoned; it should be further noted that immediately after executing Cui, Emperor Taiwu expressed regret of having done so.) In fall 450, Liu Song's Emperor Wen launched a major attack on Northern Wei, again hoping to regain the provinces south of the Yellow River, making a two-pronged attack—with the eastern prong attacking Qiaoao (碻磝, in modern Liaocheng, Shandong) and Huatai, and the western prong attacking Shancheng and Tong Pass. Under Emperor Taiwu's orders, Northern Wei forces abandoned Qiaoao while defending Huatai, and he himself headed south to relieve Qiaoao while having Crown Prince Huang head north to defend against a potential Rouran attack. The Liu Song general Wang