Cathedral – Octagon Ambulatories: Exploring the Münsterthermen

The name Aquae Granni, the Roman precursor of modern-day Aachen, points to Roman Aachen’s greatest asset: its hot springs! The mineral waters were quickly believed to have healing powers. Granni refers to Grannus, a Gallic deity associated with health and recovery. The earliest thermal baths date to around the turn of the millennium. From the outset, the Romans envisioned Aachen on a grand scale: even at its founding, the town had the air of a true city – 30 hectares in size, with wooden houses, thermal baths, and even a stone bathhouse with tiled roofs.

A City Growing Around Its Baths

In the early second century, Aquae Granni underwent a complete urban renewal. Emperor Trajan may have intended to elevate the vicus to a regional capital – a theory supported by stamped bricks and an inscription bearing his name. The original baths made way for a monumental square of more than 6,000 square metres, likely containing a forum and temple. Across the city, monumental new bath complexes were built.

Aquae Granni became one of the Roman Empire’s leading wellness centres and the only major spa in Germania Inferior.

The Münsterthermen – Southern and Northern Ambulatories of the Octagon

The scale and sophistication of these baths are evident in the Carolingian Octagon of Aachen Cathedral. You can glimpse sections of the Münsterthermen, one of the largest thermal baths in the Roman Empire, through floor windows in the Octagon’s ambulatories. In the southern ambulatory (a), large parts of the cold-water pool (frigidarium), an Early Medieval wall, and traces of a Carolingian-era earthquake are visible. In the northern ambulatory (b), remains of a hypocaust-heated room and a drainage channel can be seen. These preserved structures provide a vivid insight into Roman Aachen’s bathing culture and show how its urban planning and architecture continued to shape the city for centuries.

Discover Roman Aachen on the VIA VIA Route, 2027

The Octagon ambulatories are among the ten stops on the VIA VIA Roman City Walk route of Aachen, which links the museum exhibit with visible archaeological remains throughout the city. Along the trail, visitors encounter Roman walls, forums, baths, and late-Roman fortifications. Informative panels, multimedia displays, and encounters with Roman “characters” bring these remains to life, illustrating themes of Roman administration, bathing culture, urban planning, and the continuity of settlement from antiquity through the medieval period.

Are you ready to take a walk?

“‘The city smells of rotten eggs,’ Julia grimaces. My daughter is right. The thermal baths of Aquae Granni may be healing, but their sulphurous stench is unbearable. It doesn’t seem to bother the bathers, though. Our cart moves forward at a crawl through a crowd of shuffling people and wagons piled high with wood. ‘Most of it is for the baths,’ says a dark-skinned man walking beside us. ‘Every day, the thermae and the underfloor heating of the rich devour another piece of the forest. The baths heal the body, but not nature,’ he sighs, before vanishing again into the throng. Quintus Iulius has come up with the idea of bottling the spring water and selling it at the markets of Germania Inferior. Personally, I’m just looking forward to sliding into the warm water for a few hours — and talking with people from all corners of the Empire. Perhaps I’ll overhear some news about the situation in Rome. They seem to change emperors every few months this year. Murder and decapitation — not even the most curative water can wash that away.” – Ammulva Iucunda