while Helian Ding was engaging Western Qin's prince Qifu Mumo, putting Pingliang under siege, but although he then sent Helian Chang to Pingliang to try to persuade its defender, Helian Shegan (赫連社干, younger brother to both Helian Chang and Helian Ding), to surrender, Pingliang would not fall quickly. However, the Northern Wei general Tuxi Bi (吐奚弼) engaged Helian Ding as Helian Ding was trying to relieve Pingliang, defeating him and surrounding him at the Chungu Plains (鶉觚原, in modern Pingliang). Northern Wei forces surrounded him, and his army became hungry and thirsty. After several days, he forcibly fought his way out of the siege, but his forces mostly collapsed, and he himself was badly injured. He gathered the remaining forces and fled to Shanggui. Around the new year 431, Helian Shegan surrendered. Nearly all former Xia territory was now in Northern Wei hands. (Upon recovering Daxi Jin from Xia captivity, Emperor Taiwu punished him for his failures by temporarily making him the imperial porter in charge of serving meals, but soon pardoned him and restored him to his princely title.) (By 432, Helian Ding was no longer able to hold Shanggui, and he, after destroying Qifu Mumo's Western Qin, tried to head west to attack Northern Liang, but was intercepted by the khan of Tuyuhun, Murong Mugui (慕容慕璝), defeated, and captured. In 433, Murong Mugui, with promises of rewards, turned Helian Ding over to Emperor Taiwu, and he had Helian Ding executed.) While Emperor Taiwu was on his Xia campaign, his generals, as he instructed, crossed the Yellow River when it froze in winter 430, and quickly recaptured Luoyang and Hulao. They soon forced the retreat of the main Liu Song force, under the command of the Liu Song general Dao Yanzhi (到彥之), and trapped the remaining Liu Song troops at Huatai (滑台, in modern Anyang, Henan). A relief mission by the Liu Song general Tan Daoji could not reach Huatai, and by spring 431, Huatai fell. All the lands lost to Liu Song a year earlier had been regained. (Emperor Taiwu, in another action typical of him, rewarded the Liu Song general Zhu Xiuzhi (朱脩之), who had held Huatai for months faithfully, by giving him a daughter of an imperial clan member in marriage.) In summer 431, Emperor Taiwu made his first proposal of a marriage between the two imperial families to Liu Song. (Based on subsequent events, it