What does a basilica look like

Basilica of Constantine

Origin of the palace auditorium

The Constantine Basilica in the Roman palace district of Triers - the imperial residence and center of Roman politics since 293 AD - served as an imperial state hall, a palace auditorium for representative purposes at the beginning of the 4th century. Unfortunately, it is not known when the palace auditorium was built, whether it was at the time of the eager Gaius Valerius Diocles (Diocletian, emperor from 284 - 305) or later during the Constantinian era. On an edification during the time of Emperor Gaius Flavius ​​Valerius Constantinus, Konstantin the Elder 306 - 337, indicate the following indications:

  • Bricks used for the construction, bearing the stamp of a brick factory, which also supplied the construction site Kastel Deutz, which has been proven to date back to 310 AD. is datable.
  • A bronze coin from the year 305 AD, hidden in the brickwork of the vestibule of the palace auditorium, which was discovered during excavations.
  • Eumenius von Autun's eulogy for Emperor Constantine, given in 310 AD.

Basilica - palace auditorium

The building was named "Basilica" by local history researcher Johannes Steiner in the 19th century in reference to the traditional eulogy of Eumenius von Autun, read out in the presence of the Emperor Constantinus. Enthusiastic about the flourishing of the Trier emperor's residence, the keynote speaker “sees” the basilicas with the forum, royal buildings ”(“ video basilicas et forum, opera regia ”cf. Panegyr. VI 22 ed. Baehrens). But Protestant church buildings are also referred to as "basilicas"; therefore the Constantine basilica should be called the correct palace auditorium (aula palatina, palatium), the name for Roman secular buildings.


With its dimensions (67 m long, 27.5 m wide, 30 m high), the rectangular pillar-less building of the palace auditorium, which has been preserved today, faces south to north and is a unique Roman building north of the Alps. The enclosing walls are made entirely of bricks and mortar and with a pillar protrusion are 2.7 m thick at the base and at the top of the wall at a height of 30 m! of 3.4 m. The masonry rests on a 4 m wide and 4-6 m deep foundation made of cast concrete.
The Romans used opus caementitium = concrete (opus = building, caementum = quarry stone), a mixture of burnt lime, water, sand (mortar = mortar) and quarry stone, more and more often for their buildings, because of its properties as very rigid and freely malleable Conglomerate rock. The use of mortar to fix bricks goes back to the more recent Paleolithic and was improved by the addition of volcanic rock by the Phoenicians so that the concrete hardens under water. Brought to the Roman Empire by the Greeks, this flexible building material laid the foundation for Roman imperial architecture, for example for aqueducts (see Pont du Gard, southern France), thermal baths (see Kaiserthermen, Trier), temples (see Pantheon, Rome), sewers and port facilities.
The apse (Greek: arching) on ​​the north side, a semicircular niche-like extension with a diameter of 18 m, is flanked on the outside by two stair towers with staircases made of brick slabs arranged in a spindle shape. From the entrances on the outside of the north wall, the spiral stairs lead to the galleries at the level of the two rows of windows on the long walls and to the top of the wall.
The galleries were wooden structures triangular in cross-section, which were attached to the outside of the apse and longitudinal walls below the two rows of windows in the palace auditorium. They were used to open, close and maintain the windows and, through their external cladding, gave the impression of a massive cornice that structured the building vertically. The white-gray lime mortar plaster previously covering the entire palace auditorium was left open at the level of the galleries, which means that the stone weathered black after the galleries had decayed over the centuries. Therefore, despite the plastering that has now peeled off, the course of the galleries on the western longitudinal wall is clearly visible on the horizontal dark band below the windows.
At the southern end, three portals connected the palace auditorium with a vestibule with marble cladding and underfloor heating, of which only the foundations are evidence, as the vestibule for the new building of the Electoral Palace was demolished in the 17th century. It was an elongated vestibule oriented from east to west with an apse 11 m in diameter at the western end.
The visitor entering from the vestibule had to walk 84 m of the nave to get to the apse of the palace auditorium. Marble slabs of black hexagons and white triangles lay at his feet. The hypocaust heating below (= ceramic wall heated by warm air) warmed the huge hall:

  • five heating stoves (praefurnia) distributed on the outside of the palace auditorium conducted their hot air through heating channels lined with pumice tuff through the masonry in the plinth of the palace auditorium ...
  • ... in rooms under the marble floor. These underground heating chambers were hollow spaces filled with thousands of 1.3 m high pillars made of square brick slabs that supported the marble floor of the ancient hall. Divided into three subterranean chambers, north and south, as well as the apse, the heating of the palace auditorium could be regulated.
  • The warm air from the chambers rose on the inside of the Roman walls through hollow bricks (tubuli) behind the marble wall cladding to a horizontal connecting pipe.
  • From the cross connections on the inside, the flue gases escaped through inclined air extraction ducts. These chimneys pierce each of the nine pillars of a western longitudinal wall at the level of the window sills of the lower row of windows and diverted the exhaust air above the gallery to the outside.

Behind the triumphal arch with a height at the top of 28 m, the viewer sees the apse. The middle windows and niches of the apse are smaller than those on both sides of the apse and deliberately reinforce the perspective impression of the length of the palace hall. The man, who appeared tiny in the huge room, had to be impressed by the power of the imperial ruler, who, with his court in the colorful apse, seated on a grandstand, granted the ancient visitor an audience.


It is true that Emperor Constantine resided in several cities: Trier, Arles, Milan and others, with the palace district of Triers being the best developed.
In 330 AD Constantinus finally relocated his residence city to Constantinopolis (Istambul). Trier lost its importance as the political center of the known world forever.
After the mass migrations in the 5th century, Trier came under Franconian rule. Under the administration of the Count of the Franconian King, the palatium fell into disrepair: the gallery and roof collapsed and Roman enclosing walls served from then on as a closed courtyard for apartments and stables.
The Laurentius Church was added to the outer wall of the western wall in the first half of the 8th century.
Passed into church property in the Middle Ages, the bishops of Trier temporarily withdrew behind the thick walls of the palatium to protect them from warlike aggressors. For example, the elected Archbishop Adalbero of Luxembourg, who in 1008 successfully entrenched himself in front of the army of King Henry II behind the walls of the palatium. However, Adalbero voluntarily abdicated in favor of Heinrich's preferred candidate, Bishop Megingaud.
Arnold II. Von Isenburg and his successor Heinrich von Finstingen expanded the palatium into a fortress with four observation towers and a wine cellar in the 13th century.
Elector Lothar von Metternich (1599 - 1623) wanted to integrate the palace auditorium as one of four wings in the Electoral Palace. Because of the hardness of the masonry, the demolition work on the east and south walls came to a standstill! Only his successor, Philipp Christoph von Sötern (1623 - 1651), completed the demolition and the new building, whereby a 9 m narrow three-storey residential wing was built on the site of the former 27 m wide palace auditorium, which integrated the western wall and apse.
In the course of secularization (= secularization, detachment of the state from the ties of the church) in 1803, the Laurentiuskirche on the west wall of the palatium was demolished.
The French used the palace as a military hospital and barracks in 1810, and the Prussian military took over the palace in 1814.
In the absence of space for the Protestant parish, Frederick William IV, King of Prussia, decided to restore the Constantinian palace auditorium (Basilica of Constantine) to its original state: the east and south walls were built on the remains of the ancient walls, only a few plans and records of older findings were made. Friedrich Wilhelm IV personally took part in the inauguration ceremony of the basilica in Trier on September 28, 1856.
Incendiary bombs in the Second World War destroyed large parts of the basilica again on Aug. 14, 1944, but after being rebuilt in 1956, it opened its doors as a Protestant church.

Sources / literature

  • Ministry for Education and Culture (Ed.): "The Basilica in Trier", 1956, 73 pages.
  • Zahn, Eberhard: "The Basilica in Trier", Trier 1991, 87 pages.

for design and text: Yorck von Wartenburg, Marcus