Mathura, a prominent town of Northern India and the birth city of Sri Krishna was ruled by King Ugrasen, a Yaduvanshi ( Belonging to the Community of Yadavs). He was a great king loved by his subjects. He had two children, a son Kamsa and a daughter Devki. Kamsa was quite cruel by nature, his wickedness knew no bounds when he jailed his father and forcefully became the king of Mathura.
Love for sister Devki and Brother in law Vasudev
Though Kamsa was hard hearted but he loved his sister immensely and married her off to Vasudev, one the high ranking officers in his army. However on the day of wedding, as a result of a heavenly prediction that Devki's eighth child will be born to kill him, Kansa decided to kill his sister. On Vasudev's pleading, he put both of them in dungeons and let them live but with a promise that they will handover all their children to Kansa, only to be killed by him.
Birth of Balrama
Kansa succeeded in killing all the six new born babies of Devki and Vasudev, however the seventh child was saved by divine intervention as the child was transferred from Devki's womb to that of Rohini's, Vasudev's other wife. Thus Balram, the elder brother of Krishna was born but Kansa thought that Devki had a miscarriage.
Birth of Krishna
The birth of the eighth child of Devki, Lord Krishna was followed by a chain of dramatic events. Soon after the birth of the child, as if by a sheer miracle, all the soldiers guarding the couple fell asleep and the gates of the dungeon flew open themselves. Vasudev decided to smuggle the child safely in a basket to his friend Nand in Gokul. Since it was raining heavily, River Yamuna was all swollen and Vasudev feared that both he as well as his child will drown if he tried to cross it, however, as soon as the feet of the infant touched the river, the flow of water became normal and Vasudev was able to cross it easily. Sheshnag, the five headed serpent of Lord Vishnu protected the child with its fangs. Vasudev knew that his was not an ordinary child but a divine being. After handing his child, to his dear friend, Nand, Vasudev returned back safely with a girl child and no one got to know about it.
On hearing the news of the eighth born child, Kamsa rushed to kill the girl. He paid no heed to Devki's plead of sparing the girl. He held the child by her legs and just as he was about to bang her against the wall, the girl vanished into thin air and told Kamsa that his slayer had been born and was safe in Gokul. The girl child was none other than Yogmaya (divine illusion). The eighth child grew up as Yashoda and Nand's son in Gokul and later killed his maternal uncle Kamsa, freeing all the people of Mathura from his tyranny.