For 600 years, from 936 to 1531, the Aachen chapel was the church of coronation for 30 German kings and 12 queens.

The church became an episcopal seat in 1802 and remained so until 1825. In 1930 the diocese was reestablished.

Structure
Charlemagne began the construction of the Palatine Chapel around 792, along with the building of the rest of the palace structures.

 
The core of the Aachen cathedral is the Palatine Chapel which is surprisingly small in comparison to the later additions.

In order to sustain the enormous flow of pilgrims in the Gothic period a choir hall was built: a two-part Capella vitrea (glass chapel) which was consecrated on the 600th anniversary of Charlemagne's death. In 1978, it was one of the first 12 items to make the entry into the UNESCO list of world heritage sites, as the first German and one of the first three European historical ensembles.

Treasury
The Aachen cathedral treasury displays sacral masterpieces of the late Classical, Carolingian, Ottonian and Staufian period - among them there are some unique exhibits like the "Cross of Lothair" the "Bust of Charlemagne" and the "Persephone sarcophagus". The Cathedral Treasury in Aachen is regarded as one of the most important ecclesiastical treasuries in northern Europe.

Final Resting Place of Charlemagne
When he died in 814, he was buried in a vault in the cathedral.

In 1000, Otto III had Charlemagne's vault opened. Otto of Lomello, one of the courtiers who accompanied him, recorded the event, which is reported in the Chronicle of Novalesia, written about 1026. The account reads:
So we went in to Charles. He did not lie, as the dead otherwise do, but sat as if he were living. He was crowned with a golden crown and held in his gloved hands a sceptre; the fingernails had penetrated through the gloves and stuck out. Above him was a canopy of limestone and marble. Entering, we broke through this. Upon our entrance, a strong smell struck us. Kneeling, we gave Emperor Charles our homage, and put in order the damage that had been done. Emperor Charles had not lost any of his members to decay, except only the tip of his nose. Emperor Otto replaced this with gold, took a tooth from Charles’s mouth, walled up the entrance to the chamber, and withdrew again.
A large picture representing Otto and his nobles gazing on the dead Emperor was painted on the wall of the great room in the Town Hall.

In 1165, Emperor Frederick Barbarossa again opened the vault and placed the remains in a sculptured sarcophagus made of Parian marble, said to have been the one in which Augustus Caesar was buried. The bones lay in this until 1215, when Frederick II had them put in a casket of gold and silver. A vellum codex found interred with him was removed.