Today there are 117 bridges and overpasses in Kaliningrad. In contrast in Königsberg before the last war there were only 14 bridges. However the most well-known seven bridges over the Pregel should certainly be mentioned. We are talking about Merchandise, Green, Smith, Giblet, High, Firewood (Wooden) and Honey bridges. The whole city history involves them.
All of them were built in the Middle Ages, and at that time in order to cross the bridge, or more than that to bring goods, it was necessary to pay a toll. That is why thrifty city dwellers created a puzzle:
How to cross all seven bridges without crossing the same bridge twice?
A solution of this problem had been sought for about two centuries when in 1736 an outstanding mathematician, Leonhard Euler, became interested in the problem. He defined it as a mathematical task and proved that it could not be solved due to uneven quantity of the bridges. This result had far lasting consequences for Euler: he created a branch of mathematics that became known as graph theory on its basis, and this theory in its turn was later surprisingly applied in physics, chemistry, programming and informatics. Therefore, we can claim that the first computer is certain to have direct connections with seven Königsberg bridges.
Interestingly the story of these seven famous bridges continues at the beginning of the XX-th century. When the last emperor of Germany, and the king of Prussia, Wilhelm II heard about the puzzle, he immediately requested the city plan and a quill, and then he drew the place for an eighth bridge between the High and the Honey bridges on the plan. In 1905 this bridge was built and called the Emperor’s Bridge and since then the problem of the bridges could be solved by any pupil.
During the British bombing in August, 1944 the Emperor’s Bridge was destroyed, but in the year 2005 it was reconstructed and is called now the Anniversary Bridge.