开封 / Kaifeng
Kaifeng / 开封 is the capital city foregrounded in 169.宋太祖之死：烛影斧声，阴谋论中的人性谜团（上）. The episode treats it as both the practical center of the 陈桥兵变 and a long-term strategic compromise for the 北宋.
In the coup story, control of Kaifeng’s gates helps 赵匡胤 return from Chenqiao and complete the transfer of power. In the capital-choice discussion, the source argues that Kaifeng was easier to supply by canal and southern grain transport than Luoyang or Chang’an, but also geographically exposed and therefore dependent on heavy defense.
The city therefore anchors 开封定都取舍: economic integration and transport convenience came at the price of military vulnerability and a defensive posture the episode summarizes as “守内虚外.”
Qinji 136 adds a much earlier campaign use of Kaifeng on 刘邦’s westward anti-Qin route. The episode says Kaifeng is not large but is geographically important because the route west points toward Zhengzhou, Luoyang, Sanmenxia, and Hangu Pass. Qin defends the area heavily, so Liu Bang cannot take it quickly and continues west.