Before Lord Buddha got enlightenment he reached Rajgir in search of a teacher to solve the truth of suffering.
One day King Bimbisara learnt about Prince Siddhartha living in jungle in his Kingdom. The King personally went to see him. On meeting Prince Siddhartha , the King was taken away by the clam look and focus he had to alleviate the suffering of the humanity.
The King requested him to forgot it as it would be very difficult to realize such tall dream. The King then invited him to stay at Rajgir and even offered half of his Kingdom. Prince Siddhartha refused to the offer saying he himself has Kingdom if he so desired. He reminded the King that he left his future throne for the causes of all sentient beings.
Finally, King Bimbisara concluded that it was useless for him to convince Siddhartha and instead requested him to visit Rajgir and specially him after achieving his mission.
Months later, Prince Siddhartha got enlightenment under the Bodhi tree. Seven weeks after his enlightenment, Lord Buddha rushed to Sarnath, Varanasi to teach his first discourse to the five disciples, who once stayed together with him at Dungshrgree, Bodhgaya.
On reaching river Ganga, Lord Buddha requested the boatman to reach him to the shore.
During that era there was no bridge over River Ganga, and one need to commute through small boats. The boatman asked Lord Buddha to give fare (coins) if service of the boat was required. Since Buddha has no money, he pleaded him to reach him free. To this the boatman laughed and refused.
Lord Buddha than shown his first miracle by walking over the Ganga River and reached the other side. Seeing this the boatman was dumbfounded and shared the news to many people. Finally the news reached to King Bimbisara and instantly the king knew that it could be Prince Siddhartha .
I have visited the site near River Ganga and made a quick survey. For me I didvisualized Buddha walking over the wide Ganga River. It is nice to visualize in such a way as it happened more than 2500 years ago.
Only Buddha can do this.