Aachen Cathedral is a 1,200-year engineering palimpsest: Charlemagne’s octagon, a daring dome, then a Gothic “house of glass” grafted on without collapse. We decode the “smart” mortar, the hidden iron ring stabilizing the cupola, and the metal reinforcements that let stained glass replace stone. With laser scanning and a 3D digital twin, we reveal the sacred geometry and breakthroughs that made this monument evolve—and endure.
