It is Emperor Charlemagne´s own Palatine Chapel, which constitutes the nucleus of the Cathedral of Aachen, located in western Germany. The construction of the chapel between 793 and 813 symbolises the unification of the West and its spiritual and political revival under the aegis of Charlemagne. Originally inspired by the churches of the eastern part of the Holy Roman Empire, the octagonal core was splendidly enlarged in the Middle Ages. In 814, Charlemagne was buried here.
Charlemagne made the Frankish royal estate of Aachen, which had been serving a spa ever since the first century, his favourite abode. The main buildings of the Imperial Palace area were the Coronation Hall (aula regia – located in today´s Town Hall) and the Palace Chapel – now Aachen Cathedral. The Palatine Chapel is based on an octagonal ground plan, which is surrounded by an aisle and by tribunes above, and roofed with a dome. Facing the altar, the Emperor sat on the gallery; the Carolingian stone throne was the coronation seat of the kings of the Holy Roman Empire of German Nation from the Middle Ages until 1531. The chapel itself is easily recognizable from later additions by its distinctive structure. An atrium on the western side and a portico led to the imperial apartments. The Gothic choir and a series of chapels that were added throughout the Middle Ages created the composite array of features that characterised the cathedral.
The interior is punctuated on the lower storey by round arches set upon eight ample pillars, and on the upper storey by a gallery with eight Carolingian bronze gates. The high dome gathers light from eight open-arched windows above the drum; it was originally entirely covered with a large mosaic depicting Christ Enthroned, in purple robes and surrounded by the Elders of the Apocalypse. The present-day mosaic dates back to 1880/1881. The interior of the chapel is embellished by antique columns that Charlemagne probably ordered to be brought from Rome and Ravenna. Despite the subsequent additions, the Palatine Chapel constitutes a homogeneous nucleus.
The Cathedral Treasury in Aachen is regarded as one of the most important ecclesiastical treasuries in northern Europe; the most prominent inventory items are the cross of Lothar (about 1000 AD), made from gold and inlaid with precious stones, the dark-blue velvet chasuble with embroidered pearls, a reliquary-bust of Charlemagne made from silver and gold, and a marble sarcophagus decorated with a relief of the Abduction of Proserpine, which once contained the body of Charlemagne.