A town of many names, Colonia Ulpia Traiana developed from a tribal village to a Roman legionary frontier town, with several name changes along the way - but became a "colonia" under the Emperor Trajan and the second largest Roman town in the province of Germania Inferior. The Legions were critical to the town's development and - as the Roman legions in the west faltered and were withdrawn - so did the city itself fade.

In 13-12 B.C., the Roman general Drusus, ordered the construction of the military encampment known as Castra Vetera at the confluence of the Lippe and Rhine rivers, for the use of Roman legions serving on the Rhine. Some years later, his brother Tiberius, (later, Emperor Tiberius), who was famous for his campaigns in Germania, also served in the area. The Germanic tribe of the Sugambri, later known as the Cugerni, settled near Castra Vetera. The small military town later grew into the Colonia Ulpia Traiana, and came to be known as "Colonia Traiana."

Contrary to many other Roman cities in the tribal areas of Germany, the city or urbs of Colonia Traiana was not built on the existing oppidum of the native Cugerni; in atypical Roman fashion, the surviving tribal settlement was razed to the ground and a logical, grid-work pattern Roman city laid out afresh.

The Roman engineers meticulously planned the familiar legionary "checkerboard" pattern city ground plan of streets and housing blocks, as well as bridging the river. In the initial town, many 'blocks' were still vacant, still grassy patches of land, with a tree here and there, to be filled in as the city grew in inhabitants. Most of the land was used to build residential houses and service establishments for the many talents required by the military base.

Colonia Traiana was a trading marketplace for the near legions and the surrounding area, and trade attracted merchants and wealth. A prosperous town automatically attracted more people than a struggling village - and Colonia Traiana was prosperous. Military roads reached it, but the rivers permitted transport of almost any goods required.

The town was originally called Municipium Cugernorum, the city of the Cugerni, but texts suggest that it also had a second name, more like an abbreviated version; Cibernodurum. Apparently, Ciberni is an alternative way of spelling for Cugerni. In many ways, Colonia Traiana was a typical "legionary town" throughout the Empire. With as many as two legions quartered in the area (one of which was Legio XXIIPrimigenia), the tribes had a ready market not only for food, fodder, drink, ironworking, leatherworking, and all the needs of a military town, but the town itself became a trading crossroads for all the tribes in the area.

During the Revolt of the Batavii, the early town of Cibernodurum was destroyed, but, after Petillus Cerialis had restored order in 70 AD, the town was quickly rebuilt, and soon to acquire its "colony" status.

The nearby Roman legion, in building their legionary quarters, were experts at tile and pottery-making, and the growing population took over many of their skills as the town grew.

This map depicts the major areas of Xanten:

1. Rhine-Harbor
2. Main Temple/Capitol
3. Forum
4. Palace
5. Amphitheatre
6. Baths
In the North of the city, there were many temples to different Roman (and local) gods. The industrial quarters were located in the southwest of the city, and the main shopping district was in the west, alongside the high city walls, and in the city center.

The wealthiest part of Colonia Traiana was in the north of town, where the richest strata of society lived. Many workers in the city and imperial administration lived between the harbour and the forum (as did a lot of rich merchants). More common workers lived in the southwest, and - in the west - were the homes of the moderately to well-off middle classes.

Marcus Ulpius Traianus, better known as the Emperor Trajan (TRAIANVS) elevated this city to settlement status at some point between 98 and 107 A.D (arguably, in 100 A.D.) The town was now rebuilt on a grand scale, and had a population of about 10,000 inhabitants. After Colonia Agrippinensis (Cologne), it was the largest city in Germania Inferior province. With its area of 83 hectares, it is somewhat smaller than Cologne (96 hectares) but Cologne had fewer inhabitants.

Because Colonia Traiana was a city of importance, it looked much like most major Roman cities: it bore the signs of civilized Roman life, such as an amphitheater, multiple temples, bathhouses, and a grand temple in honor of Jupiter.

Agriculture was very important to the town, both in cultivating barley and wheat and other exportable crops, as well as cattle ranching. The people produced enough for their own use and to market products to surrounding people, as well as to the Roman armies. Together with Cologne (Colonia Agrippinensis and Trier (Treveris), Colonia Traiana was one of the three formal coloniae located in this part of the Empire.

In the turbulent third century, Colonia Traiana was apparently abandoned for a time as the German tribes attacked across Germania, but late in the century, with Rome's attempts to stabilize the German frontiers, the Emperor Constantius Chlorus re-built the military encampments around the city and strengthened its massive walls. The Thirtieth legion Ulpia Victrix was then based based somewhere in the middle of the city.

By now the town was known as Tricesima, “thirty”, named after the Legion itself.

Just like Cologne, Colonia Traiana flourished into the 4th century, and, similarly, was invaded around 355 A.D. by Germanic tribes, and then reconquered for Rome by Julian the Apostate. However, in the chaos of the late fourth and fifth centuries, its legions were withdrawn and the town, with its primary "industry" removed, dwindled.

Colonia Traiana got its later name, Xanten,from a corruption of the Latin “ad Sanctos” in rememberance of the Christian martyrs who died there, among who Saint Victor. Their graves were dated to between 358 and 363; there is no proof, however, that the town name was common before the 8th century AD.

For more information on Rome's military might, see The Roman Legions.