Ara Pacis

Step through the glass doors and the noise of the riverside traffic falls away. The air is cooler here. Light pours in through tall windows and lands on pale marble that has gone the colour of old cream. In the middle of this bright white hall stands a stone box, open to the sky above it in spirit if not in fact. This is the Ara Pacis Augustae, the Altar of Augustan Peace. It is one of the most important pieces of sculpture to survive from ancient Rome.

Let us begin with why it exists. In 13 BCE, the emperor Augustus returned to Rome after several years away in Spain and Gaul, settling the western provinces. The Roman Senate voted to build an altar to celebrate his return and the peace he claimed to have brought. It was consecrated a few years later, in 9 BCE. Rome had been torn by civil wars for decades before Augustus. Peace was not just a feeling here. It was a political message, carved in stone.

An altar sounds small, and the core of it is. Priests would have climbed the steps on the far side to make sacrifices on the altar table inside. But around that table, the builders raised a marble enclosure, almost square, with doorways on two sides. That enclosure is what you are looking at. Its outer walls are covered with carving, and nearly every surface was designed to be read like a page. Walk slowly around it before you go inside.

Start with the long side walls. Here you see a procession, people walking in a line, moving toward the same goal. These are not anonymous figures. Scholars identify members of Augustus's own family, priests in their tight caps, and officials of the state. Augustus himself appears on the south side, though his figure is damaged. Near him, many experts identify his friend and general Agrippa, with his head covered for a religious ceremony.

Now look closely for the children. This is the detail most visitors walk straight past. Small boys and girls are mixed into the procession, and they behave like real children. One little figure tugs at the clothing of the adult in front. Another seems to be hushed by a hand on its head. Roman state art rarely showed this kind of tenderness. It was deliberate. Augustus was promoting family life and the idea of a ruling dynasty that would continue into the future.

Next, look at the lower half of every outer wall. Here the people disappear, and a huge garden takes over. Curling acanthus leaves spiral across the marble in perfect, repeating scrolls. Look harder and you will find life hidden inside them. There are swans with spread wings, small birds, snakes, lizards, and even a frog or two. The message is abundance. Under Augustus, the carving suggests, the whole earth grows and multiplies. It is propaganda, yes... but it is also very beautiful.

On the short ends, beside the doorways, are four panels. Some are badly broken. The best preserved shows a seated woman holding two babies on her lap, with fruit, flowers, a cow and a sheep at her feet. Two female figures sit beside her, one riding a swan, one riding a sea creature. Who is she? Scholars still argue. She may be Mother Earth, she may be Peace, she may be Italy itself. The debate has lasted more than a century.

Another panel shows an older bearded man making a sacrifice, with a pig beside him. Many experts read him as Aeneas, the Trojan hero who, in Roman legend, fled burning Troy and founded the line that led to Rome. Others suggest he is Numa, an early king. Either way, the panel links Augustus to the deep past. Legend and history meet on these walls, and that was exactly the point.

Now step inside the enclosure. The carving changes completely. The inner walls show heavy garlands of fruit and leaves hanging between the skulls of sacrificed oxen. Shallow offering bowls hang above them. This copies the real decorations that were once fixed to temporary wooden fences around sacred places. In other words, the sculptors turned a short-lived ritual into permanent stone. Above you, the altar table rises on its steps, smaller than many people expect.

Here is a surprise. In Roman times, all of this marble was painted. The robes, the leaves, the birds would have carried bright colour. Very little paint survives, but researchers have studied the traces. The museum has at times used light projections to show how the colours might have looked. Imagine that as you stand here. The pale, quiet object in front of you was once loud and vivid.

The altar's own story after Rome fell is remarkable. It slowly sank beneath rising ground and later buildings on the Campus Martius, the old field of Mars, some distance from where it stands now. Carved fragments began turning up from the sixteenth century onward, and some travelled to collections in Florence, Paris and the Vatican. In the 1930s, engineers excavated the rest from under a palace. Water was a problem, so they froze the wet ground to dig safely beneath the foundations.

The reassembly was political too. Mussolini's government rebuilt the altar here in 1938, for the 2,000th anniversary of Augustus's birth. Some missing pieces were replaced with casts, so look for differences in texture and colour between surfaces. Outside, the long wall on the side of the building still carries a bronze inscription of Augustus's own account of his deeds, a text known as the Res Gestae. Its placement in the 1930s tied the fascist state to imperial Rome.

The building around you is modern. It was designed by the American architect Richard Meier and opened in 2006, replacing an older pavilion. It was the first major new building in Rome's historic centre for many decades, and many Romans disliked it. Some still do. Through the windows you can see the round, grassy Mausoleum of Augustus across the square. Before you leave, look from the altar to the tomb. A man who built a peace monument also built his own resting place nearby. And now, both stand together, with the river and the modern city moving quietly around them.