 In 1736 Euler solved, or rather proved unsolvable, a problem known as the seven bridges of Königsberg.The city of Königsberg, Kingdom of Prussia (now Kaliningrad, Russia) is set on the Pregel River, and included two large islands which were connected to each other and the mainland by seven bridges.The question is whether it is possible to walk with a route that crosses each bridge exactly once, and return to the starting point.