Dadu (1271) — the same event in History of Yuan and Xu Zizhi Tongjian

History of Yuan: An edict was promulgated naming the state 'Great Yuan' (大元).; Xu Zizhi Tongjian: In the eleventh month, day yihai, the Mongols…

What each source says

History of Yuan (Yuanshi), Annals · AD 1271 · 大都

An edict was promulgated naming the state 'Great Yuan' (大元).

建國號曰大元，詔曰：:誕膺景命，奄四海以宅尊；必有美名，紹百王而紀統。
Location: 元史卷7 世祖 1271年 11月

Xu Zizhi Tongjian (Continuation of the Comprehensive Mirror) · AD 1271

In the eleventh month, day yihai, the Mongols established the state name 'Da Yuan' (Great Yuan), drawn from 'Da zai Qian Yuan' in the Yijing, following the request of the Grand Preceptor Liu Bingzhong.

乙亥，蒙古建國號曰大元，取《易》「大哉乾元」之義，從太保劉秉忠請也
Location: 권179 十一月 단락179.47.0

Place: 大都

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