The Oberstadt - the upper city - is a labyrinth of narrow cobbled lanes lined with seventeenth- and eighteenth-century Hessian half-timbering, remarkably well preserved and, unusually for this kind of postcard Germany, remarkably uncrowded. The Landgrafenschloss sits above it all, and reaching it on foot means stairs, a great many of them. Locals have worked out the alternatives. Bus line 10 runs from downtown through the old town's market square and on up to the castle forecourt. Two lifts, both free, carry you from Pilgrimstein into the Oberstadt without a single step - one at Pilgrimstein 28, the other bolted into a parking deck. In summer a road train called the Schlossbahn makes the climb with a recorded commentary in several languages. When the church bells start, the sound rolls down the whole slope and into the valley.

On 17 September 1916, in the third year of the First World War, a meeting in Berlin resolved to establish the Deutsche Blindenstudienanstalt in Marburg. Alfred Bielschowsky, who ran the university's eye clinic, chaired it; Carl Strehl, then still a student, took over as general manager two weeks later and eventually directed the institute from 1927 until 1965. Blista, as everyone here calls it, is still in Marburg, and its Carl-Strehl-Schule remains the only full academic gymnasium in Germany for blind and visually impaired pupils from the fifth grade up. A century of that presence reshaped the town around it. Every traffic light in the city centre carries acoustic and tactile guidance. What Marburg has is not an institution bolted onto a town, but a town a great many blind residents simply know their way around.

Philip I, Landgrave of Hesse, founded the Philipps-Universität in 1527, and it is still the oldest surviving Protestant-founded university in the world. It is also, quite literally, the town. Marburg has roughly 73,500 residents; some 21,000 of them are students and thousands more work for the university, which is why the local line runs: other cities may have a university, Marburg is a university. The name has travelled further than the place. In 1967 laboratory workers handling tissue from African green monkeys imported from Uganda fell ill with a haemorrhagic fever nobody recognised. Thirty-one people were infected and seven died. The pathogen took the name of the town where it surfaced, and Marburg virus has been shorthand ever since for something the town itself had nothing to do with.

In 1529 Philip I wanted a Protestant political alliance, and an alliance needed its theologians to stop contradicting one another in public. He brought them up to his castle between 1 and 4 October: Martin Luther and Ulrich Zwingli, with Melanchthon, Bucer, Oecolampadius, Jonas, Brenz and Osiander filling out the room. They worked through fifteen articles and agreed on fourteen. The fifteenth asked what happens to the bread - whether Christ's body is genuinely present in it, as Luther insisted, or whether the bread is a sign and the presence spiritual, as Zwingli held. Neither man would move. The Reformation split along that line and has never entirely closed it, and the argument happened in a hall on a hill you can still walk into.

Jacob Grimm left the Friedrichsgymnasium in 1803 and Wilhelm followed in 1804, and both came to Marburg to read law. Neither was especially welcome. The university's rules disqualified applicants of their social standing, so the brothers had to petition for a dispensation simply to enrol, and the stipends that wealthier students received were closed to them. What they got instead was Friedrich Carl von Savigny, a young law professor who turned their attention from statutes toward history and philology and introduced them to Herder's idea of natural poetry - that a people's oldest stories are its truest literature. Everything the Brothers Grimm later did with fairy tales begins in that circle. The steep lanes they walked to lectures are, for the most part, the ones still standing.