Kamsa behaved more and more as a tyrant and was particularly vicious to the other wives of Vasudeva. The wives fled and hid in the various villages in the outskirts of Mathura.
Rohini who was the sister of Yashoda, fled and stayed at Gokula with Yashoda and her husband Nanda, who was the chief of the cowherds there.
The Brahma Vairvatha Purana has a very interesting story in this connection.
In the times of old, when Kashyap had married the thirteen daughters of Daksha, he would spend equal times with all his wives and keep them happy. At one such time, when he was with Kadru, the mother of all the Nagas, the eldest sister Aditi was impatiently waiting for Kashyap to come home. When Aditi realized that Kashyap was delayed because he was at Kadru's house, Aditi cursed Kadru to be born as a human.
It is said that it was because of the curse that Kadru was born as Rohini, one of the wives of Vasudeva.
(The Harivamsa gives another account for the incarnation of Rohini. The story says that Sage Kashyap stole Varuna's cow with the help of two of his wives – Aditi and Surabhi. Because of this they were cursed to be born as cowherds. Sage Kashyap was born as Vasudeva, Aditi was born as Devaki and Surabhi was born as Rohini.)
Nanda and Yashoda who were the chief of the cowherds in the village of Gokula have a very interesting story behind them.
The eldest Vasu of the heavens was Drona and his wife was the pious Dhara. Together the two of them performed penance for many many years. The only reason they performed the penance was to see Lord Narayana with their own eyes. After long years of penance they heard the glorious voice of the Lord. 'Not only would you see the Lord, you would bring him up, in your next lives!'
It is said that Drona and Dharma were born as Nanda and Yashoda for this very reason.
After the death of her first six sons, Devaki was now carrying her seventh child.
Lord Vishnu in the heavens, knew that now that the six Sadha-Garbhas were released from their bondage, the next child of Devaki could not be allowed be to be killed.
He smiled as he called for Maya, the Goddess of Illusion. 'The seventh child of Devaki is Aadi Sesha! Devaki is in prison and she cannot bring up her seventh child! You may have to transfer the womb to another mother!'
Goddess Maya understood as she came to earth. Using her powers, she transferred the child in Devaki's womb to a safe place....far away.
Devaki was shocked when she felt something different. Something had changed. As Devaki realized what it was, she broke out weeping.
In the village of Gokula, Rohini was astonished, because she was suddenly looking radiant. She felt an intense power within her and slowly realized that a child was growing in her womb....
After the birth of the six children of Devaki, Kamsa was keeping a close watch on her. He was shocked when he saw that the seventh child was no longer in Devaki's womb. Now Kamsa was even more worried. Was the child which was going to be born now, the seventh child or the eighth child? He wondered.
Fuming Kamsa decided that Devaki and Vasudeva had to be under constant vigil and put them in prison.
Rohini became the surrogate mother of the seventh child of Devaki and she gave birth to a beautiful and strong child, who was named as Rama.