Castel del Monte

Listen first. Up here on this low hill, the wind moves steadily across open ground. It carries the dry smell of wild herbs and warm stone. Below you, the Murge plateau spreads out in long folds of olive groves, wheat fields and grey rock. And in front of you stands a building that does not look like any other castle in Europe. It has no jagged ruin and no tumbled wall. It is a calm, pale shape with eight sides, sitting alone on the summit.

This is Castel del Monte, in the countryside outside the town of Andria, in the southern Italian region of Apulia. It was built in the thirteenth century for Frederick II of Hohenstaufen. He was Holy Roman Emperor and King of Sicily, one of the most powerful rulers of the Middle Ages. Construction dates to the 1240s. The building has fascinated visitors, scholars and dreamers ever since, largely because nobody is completely sure what it was for.

Start with the shape, because everything here follows from it. The main building is an octagon. At each of its eight corners stands a tower, and each tower is also an octagon. Inside, a courtyard repeats the same eight-sided form. Walk slowly around the outside and count. The number eight returns again and again, in plan, in rooms, in angles. Few medieval builders used geometry this strictly, and the effect is quiet and very controlled.

Now, a question many visitors ask as they arrive. Where is the moat? Where is the drawbridge? There are none. The castle has no deep ditch, no outer ring of walls and very few of the features you expect in a fortress. The stairs inside even climb in a direction that would not help a defender. So most historians agree that this was not mainly a military stronghold. It was something else, though exactly what is still debated.

The theories are many. Some see a hunting lodge. Frederick was passionate about hunting with birds of prey, and he wrote a long and detailed treatise on falconry. These open hills would have suited his falcons well. Others see a statement of power and learning, a building designed to show the emperor's interest in mathematics, astronomy and order. Some writers go further and link it to the stars and the seasons. Those ideas are interesting, but they are interpretation, not proven fact.

Look at the main entrance. It faces east, toward the rising sun. The doorway is framed in a reddish stone, a local coral breccia, set against the pale limestone of the walls. Above it rises a triangular pediment that looks almost like the front of a Roman temple. Yet the pointed arch below belongs to the Gothic world. This mix of ancient and medieval styles was unusual in its time. It shows a ruler who looked back to the emperors of Rome as his models.

Step inside. The castle has two floors. Each floor holds eight rooms of the same trapezoidal shape, wide on the outer wall and narrow toward the courtyard. The rooms connect to each other in a ring. On the upper floor, the windows are larger and more decorated. Notice the light. Because the rooms open in different directions, the brightness changes as you move around the circle, from soft morning light to deep afternoon gold.

Here is a detail many people walk past. This castle was built with real thought for comfort. Several rooms have fireplaces. Some towers contain small rooms that served as latrines, which was a sophisticated feature for the Middle Ages. Even more striking is the water system. Rain was collected from the roof and guided down into cisterns, so the building could store its own water on this dry hilltop. Look for channels and openings in the stone as you climb.

The climbing itself is part of the experience. Spiral staircases wind up inside some of the towers. The steps are narrow and worn smooth in the centre by centuries of feet. Put your hand on the curved wall as you go. The stone is cool, even on a hot summer day. At the top, the views open out across the plateau, and on a clear day the land seems to roll on toward the sea.

What you see today is a plainer castle than the one Frederick knew. Records and surviving fragments show that the interior was once richly finished, with marble facings, columns and coloured stone. After the emperor's death, the building passed through many hands. At times it served as a prison. Later it stood empty and neglected, and much of its decorative marble was stripped away and taken elsewhere. Look for the traces that remain, especially the columns and capitals on the upper floor.

The story turned in the late nineteenth century. In 1876, the Italian state bought the castle, and long programmes of restoration followed. In 1996, UNESCO added Castel del Monte to its World Heritage List, praising the purity of its form and its blend of influences from northern Europe, the Islamic world and classical antiquity. And there is one more surprise. If you have Italian coins in your pocket, look at the one-cent euro coin. This castle is on it.

The building also lives on in the imagination. Writers and filmmakers have been drawn to its mysterious geometry, and it is often linked to the octagonal library in Umberto Eco's novel The Name of the Rose. Locals tell their own stories too, of hidden meanings in its measurements and of the emperor watching the sky from the towers. Enjoy these tales as tales. The real mystery is simpler, and perhaps more interesting: a perfect shape with no clear purpose.

Before you leave, stand for a moment in the courtyard. Look up at the octagon of sky framed by the walls. Listen to how sound changes here, softer and closer than outside. Then walk out through the eastern gate and turn back once more. Watch how the pale stone shifts colour as the light moves. Eight sides, eight towers, one hill... and a question that has stayed open for nearly eight hundred years.