In ancient China, one man could have as many wives as he could and he could marry more than both sisters, like King Shun married two daughters of King Yao, Er-huang and Nu-ying.
In this story, the Duke Xian of Jin had wished to make Li Ji his wife, Li Ji has a sister who could accompany to the harem, there were also other Li Ji’s relatives companying her to the harem as duke’s concubines.
Before the decision was made, following the traditions, the duke consulted the divination to see if the marriage was lucky. The tortoise-shell indicated that the thing would be unlucky, but the milfoil pronounced it lucky. The duke said, “I will follow the milfoil.” The diviner by the tortoise-shell said, “The milfoil is reckoned inferior in its indications to the tortoise-shell. You had better follow the latter. And moreover, the oracle was:—
‘The change made by inordinate devotion Steals away the good qualities of the duke. There is a fragrant herb, and a noisome one; And ten years hence the noisomeness will continue.’ Do not do as you propose.” The duke would not listen to this advice, and declared Li Ji his wife. She gave birth to Xiqi, and her sister bore Zhuozi.
This caused big troubles to the state of Jin as it turned out exactly as the tortoise-shell had prophesied, and normally did the polygamy because of competition for the rights of heir among many sons.
‘When the duke was about to declare Xiqi his heir, having determined on his plans with the great officers about the court, Li Ji said to his eldest son, “The duke has been dreaming about Qi Jiang [the eldest son’s mother]; you must soon sacrifice to her.” The young prince sacrificed to his mother in Quwo, and sent some of the sacrificial flesh and spirits to the duke, who was hunting when they came. Ji kept them in the palace six days, and when the duke arrived, she poisoned them and presented them to him. The duke poured some of the spirits on the ground, which was agitated by them. He gave some of the flesh to a dog, which died; and some of the spirits to one of the attendants, who also died. Ji wept and said, “This is your eldest son’s attempt to murder you.” The son fled to the new city Quwo; but the duke put to death his tutor, Du Yuankuan.
Some one said to the son, “Explain the matter. The duke is sure to discriminate.” The son, however, said, “Without the lady Ji, my father cannot enjoy his rest or his food. If I explain the matter, the guilt will be fixed on her. The duke is getting old, and I will have taken his joy from him.” The friend said, “Had you not better go away then?” “The duke,” replied the prince, “will not examine into who is the guilty party; and if I, with the name of such a crime, go away from the State, who will receive me?” In the 12th month, on Wushen, he strangled himself in the new city.
‘Ji then slandered the duke’s two other sons, saying that they were both privy to their brother’s attempt, on which Chong’er fled to Pu, and Yiwu fled to Qu.’