Aachener Dom (Aachen Cathedral), Aachen (must see)

The Aachen Cathedral is one of the oldest in Europe. It was constructed on the orders of Charlemagne in 796. The finished building, then known as the Palatine Chapel, was consecrated by Pope Leo III in 805. Charlemagne was buried in the chapel in 814.

Antipope Paschal III canonized Charlemagne in 1165, and the chapel began drawing pilgrims from all over Europe. The traffic spawned a burst of construction activity over the next 700 years, with the choir hall, glass chapel, cupola, and steeple all being added.

Like the rest of the city, bombs heavily damaged the cathedral during World War II. Thankfully, however, the basic structure survived, and its art treasures had been previously removed for safe keeping. Bringing the cathedral back to its former glory was a 30-year, 40-million-Euro project.

The core building of the cathedral is the Carolingian Octagon, or Palatine Chapel. It was built based on the Byzantine buildings of the time. The domed octagonal interior was designed by architect Odo of Metz, the earliest known architect north of the Alps.

The upper gallery is divided by ancient columns. These came from Saint Gereon in Cologna, spolia Charlemagne brought to Aachen from Rome during the eighth century.

The geometry of the Carolingian Octagon is equally fascinating. Researchers have traced a previously unknown unit of measurement back to the structure--322.4 mm. This has come to be known as the Carolingian foot.

The eight sides of the octagon symbolize the eighth day and the resurrection of Jesus. Ten is also a reoccurring number in the structure since it symbolized perfection in Medieval architecture. For example, the diameter of the building is 100 (10 x 10) Carolingian feet, as is the dome's height.

Notable items in the cathedral include Charlemagne's throne, the Shrine of Saint Mary, the Barbarossa chandelier, and the Pala d'Oro. The church served as the coronation church for German kings for over 500 years. The precise final resting place of Charlemagne is unknown, but it is believed to be in the Persephone sarcophagus under the west tower. The actual sarcophagus is now part of the Cathedral Treasury's collection.