《资治通鉴·汉纪·汉纪五十六》
十二月，曹军到达其门，袁谭自平原撤出，退守南皮，在清河沿岸布防。
十二月，操军其门，谭拔平原，走保南皮，临清河而屯。
In December, Cao's army reached its gate. Yuan Tan withdrew from Pingyuan and retreated to guard Nanpi, deploying his defenses along the Qinghe River.
<s>[INST] Explain the meaning of this Classical Chinese passage in English: 十二月，操军其门，谭拔平原，走保南皮，临清河而屯。 [/INST] In December, Cao's army reached its gate. Yuan Tan withdrew from Pingyuan and retreated to guard Nanpi, deploying his defenses along the Qinghe River.</s>
Explain the meaning of this Classical Chinese passage in English: 十二月，操军其门，谭拔平原，走保南皮，临清河而屯。
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In December, Cao's army reached its gate. Yuan Tan withdrew from Pingyuan and retreated to guard Nanpi, deploying his defenses along the Qinghe River.
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