Back then Kaliningrad was known as Konigsberg.
If that name doesnt ring any bells then you are definitely not a mathematician.
Konigsbergs association with science and mathematics goes back to the 18th century.
The city was then a hub for science and cultural wizardry from Germany, Poland and Lithuania.
A bird’s-eye view of Konigsberg, as in late 16th century.
Konigsberg, or Kaliningrad now, is situated on the Pregel River.
As the river flows through the city, it branches out creating two large islandsKneiphof and Lomse.
Nobody could work out an answer until Leonard Euler in St. Petersburg heard about the problem.
Map of Konigsberg with the seven bridges labeled, circa 1905.
In a 1736 letter to Carl Leonhard Gottlieb Ehler, the mayor of Danzig, Eulerexpressed his displeasure:
.
Even though Euler found the problem trivial, he was still intrigued by it.
Very soon, Euler had worked out a solution.
The only thing that is important is how things are connected.
Euler observed that if every link (i.e.
a bridge) is to be crossed over only once, then each node (i.e.
a land mass) must have an even number of links attached to it.
Thats because whenever you enter one by a link, you gotta leave it by another.
Thebeauty of this argumentis that it works for any connection, no matter how large or complex.
The Old cathedral of Kaliningrad in Kneiphof island.
Honigbrucke or the Honey Bridge connects the island of Lomse to eastern Kneiphof.
This bridge is the only Kneiphof bridge that survived the Second World War and can still be seen today.
The seventh and the final bridge, Hohe Brucke, or the High Bridge, once lead to Lomse.
It was demolished and replaced by a new bridge.
An undated picture of the Green Bridge before it was destroyed.
Both the Green Bridge and Merchant Bridge was replaced by this modern overpass.
Photo credit:Padonak39/Wikimedia
Schmiedebrucke, or the Forge bridge.
Holzbrucke or the Wooden Bridge.
