After Kamsa sent so many asuras to Vrindavan in an attempt to kill Sri Krishna and Sri Balaram, they decided to invite them to Mathura for a wrestling match with great demons Chanura and Mustika . At that time Krishna came to Mathura. He and Balaram killed Chanura and Mustika and then they killed Kamsa. After they killed Kamsa, Kamsa had 2 wives Asti and Prapti and they were the daughters of king Jarasandha who was a great demon of the Magad province. They went back to their father Jarasandh and they were grief stricken and their hearts were broken and they weepingly began to proclaim to their father that Kamsa was such a noble pious righteous man, this Krishna such a rouge, he came and when our husband Kamsa was minding his own business he was not aware Krishna jumped on him and killed him by all unfair means and we will not be satisfied until the death of our husband is avenged. So Jarasandha made a vow to destroy Krishna and destroy the entire yadu dynasty. He was a very powerful asura. So, he mobilised twenty three akshahouni division of soldiers comprising all demons from entire world to help him to conquer Krishna. As you know in the battle on Kurushetra, so many solider were killed but there were only eighteen akshahounis divisions of soldiers on both sides together. Jarasandha mobilised twenty three akshahouni divisions and they attacked Mathura and Krishna, and Krishna killed all of his army, deeply uprooted them destroyed everyone except Jarasandha. He allowed Jarasandha to escape and he again went to mobilize all the demons from all over the world to come up with a huge army and again attacked Mathura. Krishna destroyed all his armies. He did this seventeen consecutive times. Now one may ask why Krishna killed his whole army but never would kill Jarasandha. The great acharyas explain that Krishna’s mission in this world is paritranaya sadhunam vinasaya duskritinam dharma samsthapanarthaya sambhavami yuge yuge. He comes for the purpose of protecting his devotees and annihilating, the miscreants, the demons. He knew that Jarasandha was such a popular and influential demon that he was getting demons form all over the world and bringing them right to Mathura so instead of Krishna travelling all over the world to kill all demons. He knew all he had to do was to kill them and let Jarasandha bring them. Whoever was left and kill them all and in this way the demons were coming right to his door.
There was a personality of the name Garga . One time it so happened that some of the members of the Yadu Dynasty ridiculed him and laughed at him. So he did tapasaya to Lord Shiva for a long time, many long years and he begged for a benediction that he would have child that would create great fear and anxiety in the Yadus. So with the benediction of Lord Shankar he begot from a woman from a yavana class, a sect most uncivilised section, of society.A son whose name was Kalayavan, who was a very powerful demon. And because he was from a Yavana untouchable class nobody liked to go close to him, very uncivilised. He mobilised a huge army of barbarians and Jarasandh arranged that one would attack from east and one would attack from west simultaneously. So Kalayavan comes with his armies from one side of Mathura and challenging Krishna to fight, and Krishna realized that while I am fighting with his armies, Jarasandh would come from other side, then the citizens of Mathura will be in a very difficult position. It would be very uncomfortable for them. So He spoke with Balaram about this and He made a plan. While all the citizens of Mathura were sleeping, Krishna called for Visvakarma, the architect of the demigods, and told him to build a beautiful city within the sea. The city had a boundary wall around it which was 96 miles and Visvakarma may build such a wonderful, beautiful, incredible palace that nobody would have seen. There are beautiful, wide high way lanes which imported many beautiful flowers like parijata from the heavenly places. Beautiful palaces all bedecked with marble and all precious jewels and gold and silver and they even brought the Sudharma the administrative parliament building of the heavenly planets of Indralok, they brought it down to be the capital of Dwarka. And after everything was beautifully constructed and all the 33 crores demigods all made contributions or gifts to make Dwarka beautiful. While all the inhabitant citizens of Mathura were sleeping, by the yogamaya potency Krishna transported everyone to Dwarka, so when they woke up in the morning they were living in this beautiful city in the middle of the ocean.
So Krishna was confident that this was a very fortified fort protected by the ocean itself and He could attempt to dealing with these demons. So when Kalyavana approached Krishna he just walked right by him and Krishna just walked very fast and he was threatening “You coward why don’t you stand and fight”. Krishna kept walking and he walked into a cave and kalyavan was thinking what type of nonsense coward He is and now hiding in a cave. When he entered the cave he saw a body sleeping on the ground. He thought him to be Krishna, what an insult, I challenged him to fight and he went to sleep and so very hardly he kicked his body but he was not Krishna but a great king named Muchukunda, who immediately arose and looked at Kalyavana with great anger and form his eyes he burnt Kalyavana into ashes. Then Muchukunda told Krishna that he was not Krishna but a great king of the name Muchukunda who immediately arose and looked at Kalyavana with great anger and form his eyes he burnt Kalyavana into ashes. Then Muchukunda told Krishna that he was a king who defended the demigods for many long years against the demons until Kartikeya the son of Shiva was born. At that time, they told me that they do not require you any more we will give you any bendiction for your seva he said the only benediction I wanted was to sleep. I haven’t slept for years and he was feared that if any other problem would take place, Indra and the demigods will wake him up so he said that I want a benediction that if any one who wakes me I will burn into ashes with my eyes. Krishna was so clever but Muchukunda was His devotee and Krishna wanted to wake him to send him back to Godhead but if He woke him then Muchukunda would look at him and if He did not burn to ashes then it would have made the demigod liars and if He would have burnt to ashes then it is not possible that He is Krishna. So He had to have somebody else to wake him up, somebody was to be burnt to ashes. Besides, Kaalayavana was a yavana and therefore it was below the dignity of Krishna to touch him with His own body or any of His weapons. So He arranged it so that Muchukunda could burn him with his glance and then He gave Muchukunda to ask for any benediction and he simply asked “Let me always remembering you with love and devotion and let me always be the servant of your devotees”.
Then Krishna went back to Mathura. and At that time, when Jarasandha attacked again, Krishna just walked away and he started chasing after Him and this time Balaram was along with Him.Krishna Balaram were walking and Jarasandha was running as fast as he can with all of his armies, akshahounis divisions of soldiers but no matter how much they ran even with their chariots and elephants and with full speed Krishna and Balarama were walking they could not reach Him and Krishna walked into a big mountain and that mountain was 80 miles tall and at that time Jarasandha and his armies searched the entire mountain but they could not find Krishna but they knew that He had not escaped so they put fire all around the mountain and lit the entire mountain on fire knowing that nobody could escape, but Krishna and Balaram from the top of the mountain they leaped over the fire 80 miles down to the ground.
Sri Krishna Balaram Ki Jai. This mountain called mount pravarshan is even today in Gujarat state called as Raivata mountain. Meanwhile Jarasandha thought that they were dead and they had nice and wonderful celebrations that Krishna Balaram were finally dead. Because Krishna ran from front of Jarasandha he gave the name Ranchor. Ranchor literaly means the one who ran form the battle like a cowhard, but when Krishna ran from battle as Ranchor He is actually a demonstration of His opulence aiswarya of renounciation. Krishna does not care of what people think of him in this regard.He is a renounciate. He allowed everyone to think that he is cowhard running way form battle because he had a very special purpose. What was His purpose? He wanted to get to Dwarka very soon because He knew that Rukmini would soon meet Him to kidnap Her and if He fought this war with Jarasandha he might be late so he walked away, jumped over the fire and entered into Dwarka.