From Provinicial City to Imperial Residence


Gaul mighty in arms has long sought to be praised and the imperial throne in the city of the Treveri, which lying close to the Rhine yet reposes deep in the bosom of peace, for she nourishes, clothes and arms the forces of the empire. Her wide walls stretch over a spreading hill: the bountiful Moselle glides by with a tranquil stream, bringing from afar the goods of all races of the earth.


This vignette of the city of Trier (French Trèves) in modern Germany by the late 4th-century AD poet Ausonius, who had known the city well as tutor to the Roman emperor Gratian in the 370s, encapsulates what then made it one of the leading cities of the empire. Above all it was an imperial residence, where the rulers of the western half of the Roman empire held court through much of the 4th century. The presence of the ‘Master of the Land and Seas and of Every Nation of Men’ and his court brought great wealth to the city, as did the presence of many senior officials and the state factories that nourished, clothed and armed Rome’s soldiers on the Rhine and elsewhere. The monuments of that imperial heyday still dominate the landscape of the city, which had long been one of the most important in Gaul.

The ‘Kaiserthermen’ (imperial baths), a huge set of baths of the 4th century AD, were probably part of the imperial palace complex. The view shows the interior of the apse of the caldarium, the hot room of the baths.

© KFS/Imagebroker/

The Treveri had been a powerful pre-Roman Gallic tribe, resisting Julius Caesar but later supplying cavalry units for the Roman army. As its Roman name Augusta suggests, the city came into being under the first emperor; dates from timber piles of the first Moselle bridge indicate it was in the 10s BC. Situated on the valley floor between the right (eastern) bank of the Moselle and the hill of the Petrisberg, the central area of the city acquired its street-grid under Augustus. In the course of the 1st and 2nd centuries it was endowed with an exceptional set of public buildings centring on a huge forum and basilica complex raised on a cryptoporticus, a large covered gallery. Just by the bridgehead a set of public baths, matching in scale those of other leading cities of the empire and even of Rome itself, was built at the start of the 2nd century; some of the baths’ structures, known as the ‘Barbarathermen’, remain visible. To the east, the Petrisberg was crowned with a large amphitheatre, its masonry walls retaining earthen seating banks; chambers under the arena furnished the elements for the spectacles. The greatest undertaking was the construction from the later 2nd century AD of a set of walls over 6 km (almost 4 miles) long and enclosing 285 ha (704 acres), the largest of that date in the western empire. The massive, unfinished north gate, the so-called ‘Porta Nigra’, survives to this day.

The ‘Porta Nigra’, the main north gate of the city. Constructed from the later 2nd century AD, it remained unfinished. The modern name meaning the ‘black gate’ derives from the colour of the weathered sandstone.

© Mikhail Markovskiy/

Trier’s position behind the Rhine frontier but linked to it by the Moselle marked it out as of strategic significance. From the 1st century AD it had been the seat of the Procurator (financial administrator) for the provinces of Belgic Gaul and the Germanies. As the pressures on the Rhine increased through the 3rd century AD so did the importance of Trier, with emperors increasingly residing near the frontiers rather than at Rome. This status was confirmed at the start of the 4th century by the construction under Constantine I (AD 306–37) of the principal imperial residence north of the Alps, consisting of a complex of buildings covering the northeastern quadrant of the city. The most important to survive is the ‘Basilika’ (a modern name), an immense, aisleless rectangular building (67 m/220 ft long and 30 m/98 ft high) with two rows of large windows and a projecting apse, built under Constantine. This was clearly the imperial audience hall (aula palatina), where the emperor would sit enthroned beneath the arch of the apse. Today austere bare brick, in antiquity the interior would have been brilliant with cut marble and coloured mosaic.

The ‘Basilika’, the interior of the huge audience hall of the early 4th-century AD imperial palace (the ceiling is a modern reconstruction). This would have been the setting for imperial ceremonial such as receiving high officials and embassies.

Bildarchiv Monheim/akg-images.

South of the ‘Basilika’ lay the ‘Kaiserthermen’, a huge set of baths, substantial parts of which survive. They never in fact functioned as baths and were later partly demolished and put to some other, unidentified use. The cathedral (Dom) and neighbouring Liebfrauenkirche overlie the remains of an imposing cathedral complex built in the 320s and consisting of two great basilican churches side by side, which replaced part of the palace. These perhaps were in part the work of St Helena, mother of Constantine I, relic-hunter and long-time resident of the city. Northeast of this in turn probably lay a circus or hippodrome, the setting for some of the public spectacle of an imperial residence. Little is yet known of the installations of the senior officials or the state factories supplying the armies.

Emperors ceased to reside at Trier towards the end of the 4th century and shortly afterwards its administrative functions were removed to Arles. Nevertheless, it remained the greatest city of northern Gaul and enough of a prize to be sacked several times in the course of the 5th century, while remaining a major Christian focus.

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