Some of my students gave a presentation today on graph theory, and talked about the Bridges of Königsberg. Königsberg was founded in 1254 and is part of the Russian enclave Kaliningrad. And it shows up in math talks because of its bridges. As a brief background, the Pregal River runs through the city and splits in two; there’s also an island, so there are four different land masses. You can kind of see this in the following map from 1652 (which appears in almost any math talk on the subject): Click for the picture, and also for a cool satellite photo of Königsberg today (which I hid behind the jump because it takes a few seconds to load).