Krishna Kills Kansa   

As per the Puranas,the legend says-Mathura, a prominent place in Northern India which is the birth place of Shri Krishna,was ruled by King Ugrasen,who belonged to the Community of Yadavs(Yaduvanshi).

He was a beloved king,who had two children, a son Kansa and a daughter Devki.Kansa was very cruel and wicked,who jailed his father and forcefully became the king of Mathura.

Kansa loved his sister very much and got her married to Vasudev,who was the high ranking officers in his army. However on the day of wedding,a heavenly prediction received that that Devki’s eighth child will be born to kill Kansa.So Kansa decided to kill his sister Devki but on Vasudev's pleading,he jailed them and let them live on a condition that they will handover all their children to Kansa, who will be killed by Kansa.

Kansa succeeded in killing the first six new born babies of Devki and Vasudev, however the seventh child was saved by divine intervention.The child was transferred from Devki’s womb to that of Rohini,who was the other wife of Vasudev.Kansa thought that Devki had a miscarriage.The born child was Balram,the elder brother of Krishna.

The birth of the eighth child,Lord Krishna was a great miracle.Soon after his birth,all the guards of the jail fell asleep and the gates of the jail got opened themselves. Soon,Vasudev decided to pass on the child in a basket to his friend Nand,staying in Gokul.
 

During the heavy rains,the River Yamuna started to flood and Vasudev feared that he and his child will get drowned if he tried to cross it.However, as soon as the feet of the child,Krishna touched the river water,the water level 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 was aware of his miraculous child,who was 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,Kansa rushed to kill the girl by holding her legs and was about to bang her against the wall,but the girl vanished into thin air.The girl was the Yogmaya (divine illusion),who told Kansa that his slayer had been born and was living safelyu in Gokul.
 

The eighth child,Shri.Krishna grew up as Yashoda and Nand’s son in Gokul and later killed his maternal ,cruel uncle Kansa.The inhabitants of Mathura blessed Krishna for relieving them from the cruel king,Kansa.