Though its slightly eccentric exterior hints at the building’s unique riches, the dark, Byzantine interior of Aachen’s Dom nevertheless comes as a surprise. As you enter the cathedral through the massive, twelve-hundred-year-old bronze doors you’re immediately presented with its great glory, the octagonal palace chapel built for Charlemagne and inspired by the churches of San Vitale in Ravenna and Little Hagia Sophia in Istanbul. It was the first domed church north of the Alps and though it was the work of Otto von Metz, Charlemagne himself contributed his own ideas to the design. If you can, take the guided tour as much of the interior is off limits for casual visitors and you’ll only gain the most superficial impressions without it. In particular, it’s only on the tour that you’ll see the modest marble Imperial Throne in the upper gallery which was used for coronations for six centuries, from Otto I in 936 to Ferdinand I in 1531. At the time of writing, ongoing restoration work meant parts of the octagon were obscured from view.

The vast twelfth-century gilded Barbarossa chandelier, which hangs low in the centre of the octagon, catches the eye, along with the nineteenth-century mosaics inside the dome high above; but the octagon’s marble pillars are altogether more ancient, having been brought to Aachen from Rome and Ravenna with the permission of Pope Hadrian I. So prized are they that French troops hauled 28 of them off to Paris in 1815, where four can still be seen in the Louvre. As the burial place of Charlemagne and a place of pilgrimage, the cathedral was embellished over the centuries with various chapels, and in the fourteenth century a soaring, light-filled Gothic choir – the so-called “Glass House of Aachen” – was added to ease the crush of visiting pilgrims. It houses the gilded thirteenth-century shrine that contains Charlemagne’s remains. The choir’s original stained glass was destroyed by hail in 1729; the present windows are post-1945, and replaced glass destroyed during World War II.