For 10 points, name this city that served as a capital of the Northern Song dynasty and still contains a small population of Chinese Jews.
During Subotai's siege of this city, its defenders used iron chains to lower a devastating explosive called the "heaven-shaking thunder-crash bomb" into the enemy's trenches. A device in this city made use of a "celestial ladder," the first known chain-drive mechanism, that powered its armillary sphere; that was the astronomical (*) clock tower designed here by Su Song. Its cultural landmarks include an octagonal-based pagoda named for the color of its glazed bricks, the Iron Pagoda. This city was sacked in the Jingkang Incident, in which emperors Qinzong and Huizong were both abducted, forcing the capital to move to Lin'an while this city became the southern capital of the Jin. For 10 points, name this city that served as a capital of the Northern Song dynasty and still contains a small population of Chinese Jews.
During Subotai's siege of this city, its defenders used iron chains to lower a devastating explosive called the "heaven-shaking thunder-crash bomb" into the enemy's trenches.
Kaifeng [or Dongjing; or Bianjing]