It’s Leonard Euler’s 314th birthday today. In network circles the grandfather of graph theory is perhaps best known for his 1735 solution to the problem known as the Seven Bridges of Königsberg. Using novel graph theory techniques Euler was able to show that a route across the seven bridges without crossing the same one twice was impossible.
Euler’s work was fundamental for graph theory and I find it delightful to overlay the original problem statement over the roads and bridges that make up Königsberg, now Kaliningrad, today.