Between a.d. 792 and 805, as part of his now vanished palace, Emperor Charlemagne built what’s called the Palatine Chapel, or the Octagon. This eight-sided, two-tiered, domed structure clad in multi-colored marbles is the first part of the cathedral that you enter, and the oldest. Consecrated by the Pope in 805, it was the first large church building to be constructed in western Europe since the demise of the Roman Empire. Stylistically it’s an amalgamation of classical, Byzantine and pre-Romanesque architecture. Charlemagne’s throne, the simple stone Königsstuhl, one of the most venerable monuments in Germany, is on the chapel’s second level and can only be seen on a guided tour.

From 936 until 1531, when the ceremony moved to Frankfurt, Holy Roman Emperors were crowned in this cathedral. Stylistically it’s an amalgamation of classical, Byzantine, and pre-Romanesque architecture. Much sympathetic restoration work has been done over the centuries, including the cupola mosaic, depicting a scene from the Book of Revelation in Byzantine style but redone in the 19th century. The soaring Gothic style, imported from France, was used when the cathedral’s Choir and Sanctuary were constructed in the 14th century. Visitors aren’t allowed to enter this section, but can view its two major treasures: the Charlemagne Reliquary, an ornate gold box crafted around 1215 for the emperor’s remains; and the stunning gold Pulpit of Henry II (ca. 1014), decorated with antique bowls, ivory carvings, chess figures, and reliefs of the evangelists. The Domschatz (Cathedral Treasury) is worth visiting to see the famous silver and gilt bust of Charlemagne and other religious treasures.