East side of Aachen Cathedral. The construction of Aachen Cathedral begun by Charlemagne around 796 AD. Its remarkable Palatine Chapel, with its octagonal central plan and Byzantine-inspired mosaics, is one of the finest surviving examples of Carolingian architecture. The building is primarily Gothic, with its impressive façade decorated with 50 statues of German rulers, including Charlemagne. In the 17th and 18th centuries, it was extensively remodeled in the Baroque style, giving the upper façade its distinctive ornate appearance.