Aachen Cathedral

Step inside, and the first thing you notice is the shape of the space. It is not a long nave pulling your eye toward an altar. It is a ring. The walls fold around you in eight sides, and above your head the light gathers in a high golden dome. The air is cool and smells faintly of stone and candle wax. Your footsteps sound different here, softer and rounder, as if the building is holding them close.

This eight-sided heart is the Palatine Chapel, built for Charlemagne, the king of the Franks who united much of western Europe and was crowned emperor in Rome in the year 800. He chose Aachen as his favourite residence, partly for its warm springs. Around the end of the eighth century, he ordered a palace complex here. This chapel was its spiritual centre. Most of what surrounds you in the octagon has stood for more than twelve hundred years.

The name connected with its design is Odo of Metz, though we know very little about him beyond that name. What we do know is the model. Charlemagne's builders looked south, to the churches of Italy, and especially to San Vitale in Ravenna, an eight-sided church from the age of the Byzantine emperors. The idea was clear. A new Christian emperor in the north deserved a building that echoed the old empire of Rome.

Now look at the columns on the upper levels. Many of them are not local stone. They are antique columns, taken from Roman buildings in Italy and carried across the Alps. Reusing old materials this way was a statement. Here is a surprise many visitors miss: some of these columns were taken away to Paris during the Napoleonic era. Not all of them returned, so the set you see today is partly a reassembly.

Lift your eyes to the dome. The glittering mosaic up there looks ancient, but it is not. The original Carolingian decoration was lost long ago. What you see is a nineteenth-century recreation, made with gold-backed glass tiles to give a sense of how the chapel may once have shone. It is still a powerful effect. On a bright day the gold seems to move as clouds pass outside.

Hanging in the centre of the octagon is a huge wheel of gilded metal, the Barbarossa Chandelier. It was a gift from the emperor Frederick Barbarossa in the twelfth century. Its ring of towers and gates is meant to suggest the heavenly Jerusalem, the holy city described in the Bible. Imagine it lit with dozens of candles, swaying slightly above the crowds below. It hangs where you can study it closely from the floor.

Charlemagne died in 814 and was buried here, in his own chapel. Over the following centuries his tomb drew pilgrims, and his reputation grew into something close to legend. In the twelfth century, under Barbarossa, Charlemagne was even declared a saint, though that step was never recognised by Rome. His remains now rest in a golden shrine in the choir, completed in the early thirteenth century.

Up in the western gallery stands one of the most remarkable objects in the building — a plain throne of marble slabs. It is known as Charlemagne's Throne. From the tenth century to the sixteenth century, around thirty German kings were crowned in Aachen and then sat on this seat. It looks surprisingly modest. No gold, no jewels. Just old stone and a set of steps. You can only reach the gallery on a guided tour.

Now turn toward the east, and the mood changes completely. Beyond the dark, heavy octagon rises the Gothic choir, finished in the early fifteenth century. It is a tall hall made almost entirely of glass. Locals have long called it the glass house of Aachen. On a sunny afternoon, coloured light pours across the floor. Notice how the walls seem almost to disappear between the thin stone supports.

Why build such a large new space? Pilgrims. Aachen holds relics that medieval Christians believed were linked to Mary, to Jesus, and to John the Baptist. Every seven years they are brought out and shown to the public in a great pilgrimage. In the Middle Ages, huge crowds came for it. The choir gave the church room to receive them, and to house the golden Marian shrine that keeps these relics today.

Before you leave, go back to the main entrance and find the heavy bronze doors. They date from Charlemagne's time. Locals tell a playful story about them. According to legend, the people of Aachen ran out of money and accepted help from the devil. His price was the first soul to enter the finished church. The townsfolk sent in a wolf. The furious devil slammed the door and tore off his thumb. Run your fingers over the lion-head handle, and some say you can feel it there.

The cathedral was among the very first places in the world named a UNESCO World Heritage Site, in 1978, and it was the first in Germany. It is easy to see why. Few buildings let you stand in one room and pass from the world of Charlemagne into the late Middle Ages in a few steps. The octagon and the choir sit side by side, eight centuries apart, but joined as one church.

If you have time, the cathedral treasury nearby holds some of the finest medieval goldwork in Europe. Among its pieces are a jewelled processional cross and a silver and gold bust associated with Charlemagne. It needs a separate visit, but it completes the story you have just seen here. Many people find the treasury helps the church make more sense.

As you walk out, pause in the small square outside. Listen to the bells, the voices, the clatter of the old town around you. Look back once at the mix of shapes — the round dome, the sharp Gothic windows, the later towers and chapels added over the centuries. This is not one building from one moment. It is a church that grew slowly, layer by layer, around one emperor's chapel. And it is still in use today.