The city of Aachen stands 40 miles (64 kilometers) southwest of Cologne on the River Wurm, a tributary of the Roer, in the German stare of North Rhine-Westphalia. The Romans knew the place as Aquisgranum, famous for its health spas since the first century a.d. The Merovingian kings, who ruled the Franks from a.d. 481 to 751, held court there, but the town enjoyed great eminence during the Carolingian dynasty, especially under Charlemagne (reigned 768–814). His Palatine Chapel, now the central element of Aachen Cathedral, is the finest surviving example of Carolingian architecture. This architectural jewel copied the centrally planned Byzantine church of San Vitale at Ravenna, Italy (525–548), clearly demonstrating one way in which building ideas are transmitted between cultures. The ability of its northern builders to assimilate a southern European style was in itself a considerable achievement.
Charlemagne succeeded his father, Pepin the Short, as king of the Franks in 768. The first strong secular ruler in Europe since the ancient Roman Empire, he was in theory—but only in theory—subordinate to the pope, a relationship symbolized by his coronation by Pope Leo III as Holy Roman Emperor on Christmas Day 800. Six years earlier he had established his residence and Court at Aachen, the town where he was born. In 792, he commissioned Bishop Odo of Metz to design and build the royal complex, 50 acres (20 hectares) in area: the palace, law court, and, of course, the Palatine Chapel. Einhard (who was also Charlemagne’s biographer) was appointed as works supervisor. Wanting to imitate the grandeur of the imperial Roman rulers, the king had looked for precedents. Historians have suggested that his palace was based on several models, Constantine’s palatine court (ca. 310) in Trier, Germany, among them. Charlemagne also had been to Ravenna on Italy’s northern Adriatic coast, where he had been dazzled by the glorious Byzantine buildings. Kenneth Clark opines that, when the Frankish king saw the scintillating mosaics in San Vitale, he “realized how magnificent an emperor could be.” Returning to Aachen, Charlemagne gave instructions for a replica to be built as his private chapel.
Constructed at the southern end of the palace complex on the site of an earlier church, the domed octagonal Palatine Chapel was built between 796 and 804. It was consecrated by Pope Leo III in 805 to serve as Charlemagne’s chapel, a reliquarium for his collection, and a church for members of the royal court. It is 54 feet (16.5 meters) in diameter and 124 feet (38 meters) high—at the time the largest dome north of the Alps. Of course, beautiful as it is, in the circumstances Odo’s building could never have been a perfect replica. Architectural ideas are transmitted by several means: traveling architects, craftsmen, or patrons; images of buildings; and published theories. None is ideal. Images cannot convey the spatial aspects of buildings, and a visit to a building, no matter how perceptive and prolonged, leaves the visitor with mere impressions only. For those reasons, San Vitale lost a good deal in the translation, so to speak, even if Charlemagne imported columns and marbles from Ravenna and Rome and Byzantine craftsmen to assist with the work. Moreover, the refinement of the Italian church had been achieved after years of experiment with indigenous structural and decorative systems. Nevertheless, the Palatine Chapel at Aachen is an extraordinary advance upon preceding Carolingian buildings.
It is much sturdier than San Vitale, having an unmistakably Roman structure. Like early Roman churches, it was approached from the west through a huge symmetrical atrium (said to have held 7,000 people), the well-defined entrance to the octagon flanked by towers with turret staircases leading to an upper level. Above the entrance was a place from which the emperor could appear to his people. None of the atrium survives. The octagonal central space of the original chapel is crowned with a lofty mosaic-faced dome constructed as a series of groin vaults: opposite the entrance, on both levels, was the sanctuary. The octagon is surrounded at the lower level by an ambulatory with a groin-vaulted dark sandstone ceiling. Those vaults, remarkable for the absence of transverse arches—Odo’s own innovation—are supported at the angles of the octagon on large piers that also carry a semicircular dividing arcade. The upper level of the ambulatory is roofed with an annular barrel vault and separated from the octagon by a screen of two pairs of superimposed marble, porphyry, and granite columns within wide arched openings. At right angles to the main axis of the chapel, and reached at both levels through the sanctuary, were once mirrored north and south annexes.
On the decision of the members of the court, although he wished to be buried at St. Denis, Charlemagne’s remains were interred in the Palatine Chapel in 814. Thereafter, until 1531, it became the imperial coronation church. From 1355, to accommodate the enormous traffic of pilgrims, the choir was rebuilt in the Gothic style, several chapels and a narthex were added, and the building became Aachen Cathedral. It was dedicated in 1414. The original mosaic on the interior of the dome was replaced by one Salviati, a Venetian, between 1870 and 1873. The cathedral was designated a UNESCO World Heritage site in 1978. A restoration program began in 1995.