Colonia Claudia Ara Agrippinensium

Put your hand on a piece of old Roman wall in Cologne and you will feel it. The stone is cool and rough, and the joints between the blocks are worn smooth. Above you, trams hum and church bells ring. Under the shops, cafés and cathedral spires, there is another city, buried and patient. Its full name is Colonia Claudia Ara Agrippinensium. Today that Roman name has shrunk to a single word: Cologne.

The long name works almost like a sentence. Colonia means a Roman colony, a town with full Roman status. Claudia honours the emperor Claudius, who granted that status. Ara means altar, the religious centre of the settlement. Agrippinensium refers to the people of Agrippina. The modern German name, Köln, and the English name, Cologne, both come from that first word. So every time someone says the city's name, they still say Latin.

The story begins before the colony existed. In the late first century before Christ, the Roman general Marcus Agrippa moved a Germanic tribe called the Ubii. They were allies of Rome, and they had lived on the eastern bank of the Rhine. Rome settled them on the western bank, here, as a friendly buffer on the frontier. Their settlement became known as the town of the Ubii. It sat on a slight rise above the river, a site that stayed dry and easy to defend.

Now comes the person behind the name. Agrippina the Younger was born here in the early first century. She was the granddaughter of that same Agrippa, and she had a remarkable political career. She married her uncle, the emperor Claudius. She was also the mother of the future emperor Nero. Historians generally credit her influence for what happened next. Around the year 50, Claudius raised her birthplace to the rank of a colony. A woman's birthplace became one of the leading Roman cities on the Rhine.

The colony grew into a regional capital. It became the seat of the governor of Lower Germania, the Roman province along the lower Rhine. Soldiers, merchants, officials and craftsmen came here from across the empire. Ships carried wine, oil, pottery and stone along the river. The town received a stone wall, gates and a grid of straight streets. If you look at a map of Cologne's old centre, some modern streets still follow the old Roman lines.

Here is a detail many visitors miss. Cologne's water did not come from the Rhine. The Romans built a long aqueduct from the Eifel hills to the south-west. It ran for close to one hundred kilometres, mostly underground, and it carried fresh spring water into the city. Over the centuries the channel filled with hard mineral deposits. In the Middle Ages, builders cut out this material and reused it like polished stone in churches across the region.

The Roman city also had a rich workshop life. Cologne became known for fine glass. Roman glassmakers here produced delicate bottles, cups and bowls, some with coloured threads and patterns. Many of these pieces survived in graves outside the walls, because Roman law placed burials outside the town. Pottery, jewellery, coins and carved tombstones came out of the same ground. Together they show ordinary lives: a soldier from far away, a family mourning a child, a trader who did well.

The second surprise lies under the city hall. Excavations in the twentieth century uncovered the remains of the Praetorium. This was the palace of the Roman governor, the administrative heart of the province. Its foundations survive beneath the later medieval and modern buildings. In other words, the people who govern Cologne today work on the same spot where Roman governors once worked. A large new archaeological quarter is being developed in this area, so access to the remains depends on current construction.

Not far away, near the cathedral, you can also find traces of the Roman harbour road and parts of the town's north gate. One arch from that gate stands as a reminder of where the walls once closed the city. Walk slowly here. The cathedral itself stands inside the old Roman town. Early Christian buildings rose on this site long before the Gothic towers. Cologne's Christian history and Roman history grow from the same soil.

Next to the cathedral is the Romano-Germanic Museum. Its most famous treasure is the Dionysus mosaic, a large floor from a wealthy Roman house. It shows scenes linked to Dionysus, the Roman and Greek god of wine and celebration. Workers found it in 1941 while digging an air-raid shelter during the Second World War. The museum was later built over the mosaic, so it still lies in its original place. Part of the collection may be shown in another location while the building is renovated.

One of the most charming survivors is the Roman tower on the north-west side of the old town. It was a corner tower of the city wall. Its outer face carries decorative patterns made from stones of different colours. You can see circles, lines and shapes that look almost like a game board. The Romans built walls for defence, but here they also made a statement. They wanted visitors to see a city that was secure, wealthy and confident.

As Roman power weakened, the city changed hands. In the fifth century, the Franks took control, and Roman Colonia slowly became a Frankish and then a medieval city. But the old layout did not disappear. Medieval builders used Roman walls, foundations, stones and street lines. During the Second World War, bombing destroyed much of Cologne. Reconstruction and new building work then uncovered more Roman remains. Destruction above ground often opened windows into the past below.

So as you walk through the city, look down as well as up. Notice the change in stone colour at the base of an old wall. Notice a glass panel in a pavement, or a modest sign beside a fragment. Each one marks a place where the Roman town comes close to the surface. Take a moment beside the river, too. The Rhine still runs past the place where the Ubii settled, and the city still carries their Roman name.