Domus Transitoria

The air changes first. As you step down from the bright Palatine Hill, the warmth of the Roman sun falls away. The air turns cool and slightly damp, with the mineral smell of old brick and wet stone. Your footsteps sound softer here. Above you, the ruins of a later palace press down like a lid. You are now standing below the ground level of imperial Rome, inside rooms built for one of its most famous emperors, Nero.

This is the Domus Transitoria, which means, roughly, the house of passage. It was Nero's first great palace, built in the early years of his reign in the first century. The name tells you its purpose. The complex was planned to link the imperial properties on the Palatine Hill with the gardens and estates on the Esquiline Hill, across the valley where the Colosseum now stands. It was less a single house and more a chain of buildings, gardens and corridors.

That ambition did not last long. In the year 64, a great fire swept through Rome for days. Large parts of the city burned, and Nero's new palace burned with it. Here is the first surprise. Nero did not simply repair it. He used the cleared land to build something even grander, the Domus Aurea, or Golden House. So the rooms around you are the opening chapter of a much more famous story, a palace that existed only for a short time.

Why does anything survive at all? The answer is above your head. Later emperors filled in and built over Nero's rooms. The Flavian dynasty, who came to power soon after Nero's death, raised their own enormous palace on top. Domitian's palace used these older spaces as foundations. By burying the rooms, the builders protected them. What looks like destruction became a kind of storage, and it kept colour and marble hidden for many centuries.

Look around at the walls and floor. The core structure is Roman brick and concrete, the workhorse materials of imperial building. But this was never meant to be seen bare. The surfaces were once covered in precious stone. Romans prized coloured marble brought from across their empire. Deep red and purple porphyry came from Egypt. Warm yellow stone came from North Africa. Green stone came from Greece. Each colour was a statement of wealth and reach.

The most celebrated space here is a nymphaeum, a fountain room dedicated to water nymphs. In Roman palaces, a nymphaeum was a place of cool water, shade and display. Picture a wall where water ran down over steps and niches, catching the light. Picture the sound of it, filling the room with a steady, gentle noise. Guests would have reclined nearby, eating and talking, while the water moved in front of them. It was theatre as much as architecture.

The floors and wall panels used a technique called opus sectile. That is Latin for cut work. Instead of tiny mosaic cubes, craftsmen cut thin pieces of marble into exact shapes — circles, leaves, stars, interlocking geometric patterns. They fitted the pieces together so tightly that the joins almost vanish. This needed great skill and a great deal of money. Where fragments remain, look closely at the edges. You can still see how precisely each shape was cut and placed.

Here is the second surprise. Not everything that once decorated these rooms is still here. Excavations in the eighteenth century uncovered parts of the complex, and much of the decoration was removed in that era, as was common practice then. Later digs in the early twentieth century brought more to light. Some painted fragments recovered over time are now displayed in museums, including the Palatine Museum nearby. So the rooms you see are only part of the picture.

The paintings that do survive show how Nero's court liked to live. Roman wall painting of this period mixed delicate architectural fantasies with small figures and scenes from myth. Thin painted columns frame imaginary views. Tiny figures stand in airy spaces. Some decoration also used gilding and glass paste, which would have shone in the light of oil lamps. Try to imagine these rooms at night, with flames moving across gold, marble and painted plaster.

The modern visit uses technology to fill the gaps. Visitors move through the rooms in small groups, and digital projections and virtual reality headsets help rebuild what has been lost. In one moment you see bare brick. In the next you see colour, light and running water. This approach is honest about the ruin. It does not pretend the marble is still in place. Instead, it shows you two layers of time at once — the place as it is, and the place as it was.

Think, too, about the person who ordered all this. Nero became emperor while still a teenager. Ancient writers, who often disliked him, describe him as a lover of art, music and spectacle. They also blamed him for the excesses of his reign. Many historians today treat those ancient accounts with caution, because they were written by his enemies. What is certain is the scale of his building. These rooms show a ruler who wanted his home to be a stage.

As you move through the site, notice the sense of depth. You are below the Flavian palace, which itself is a ruin open to the sky above. Rome is full of these layers. A church sits on a temple. A palace sits on an older palace. Streets run over buried streets. Down here, you are inside one of those layers. The bricks overhead belong to one century. The floor beneath your feet belongs to another.

Before you climb back into the daylight, pause for a moment. Listen to the quiet of these rooms. Once, water ran here and guests laughed over dinner. Then fire came, and then earth and new walls sealed it all away. When you step outside, the heat and light of the Palatine will return. Look down at the ground as you walk. Somewhere beneath the gravel and the grass, other rooms are still waiting.