Trier rose in importance during the Empire's third-century crisis, as the chief city of the province of Gallia Belgica.
From 271 to 274 AD, Trier was the second city of the breakaway Gallic Empire, at first under Postumus, who was proclaimed in Cologne, then under his ephemeral successor, Victorinus, who made his base at Trier, where he had rebuilt a large house with a mosaic proclaiming his position as tribune in Postumus' Gallic Praetorian Guard;[4] the city served again as capital under the emperors Tetricus I and II.
In 326, sections of the imperial family's private residential palaces were extended and converted to a large double basilica, the remains of which are still partly recognisable in the area of the Trier Cathedral (Trierer Dom) and the church "Liebfrauenkirche".
[10] A demolished imperial palace has left shattered sections of painted ceiling, which scholars believe once belonged to Constantine's young wife, Fausta, whom he later put to death.
[11] From 318 onwards Trier was the seat of the Gallic prefecture (the Praefectus Praetorio Galliarium) which governed the western Roman provinces from Morocco to Britain.
[citation needed] The city became definitively part of Frankish territory (Francia Rhinensis) around 485; the last Roman administrator of Trier was Arbogast.
[14] As a result of the Treaty of Verdun in 843, by which the grandsons of Charlemagne divided his empire into three parts, Trier was incorporated into the Kingdom of Lorraine (Lotharingia).
After the death of Lothair II, ruler of Lorraine, Trier in 870 became part of the East Frankish Empire, later called Germany, under Henry I.
[15] Many abbeys and monasteries were founded in the early Frankish time, including St. Maximin, St. Martin, St. Irminen, St. Maria ad Martyres/St.Mergen and others.
[19] Medieval legend, recorded in 1105 in the Gesta Treverorum, makes Trebeta son of Ninus the founder of Trier.
[20] Also of medieval date is the inscription at the facade of the Red House of Trier market, being mentioned in the Codex Udalrici of 1125.
The Archbishop of Trier was, as chancellor of Burgundy, one of the seven Electors of the Holy Roman Empire, a right which originated in the 12th or 13th century, and which continued until the French Revolution.
[25] From 1581 until 1593, intense witch persecutions, involving nobility as well as commoners, abounded throughout this region, leading to mass executions of hundreds of people.
Warfare reached the city as part of the French–Habsburg rivalry and the conflict between townspeople and the archbishop Philipp Christoph von Sötern.
Despite their efforts, they were forced to leave by Imperial troops after the Battle of Konzer Brücke in 1675[27] In 1684, with the War of the Reunions, an era of French expansion began.
King Louis XIV of France personally issued the order for these acts of destruction but also gave the command to spare the city of Trier.
After a short period of peace, the War of the Polish Succession started in 1734; the following year Trier was again occupied by the French, who stayed until 1737.
In 1801, Napoleon Bonaparte signed a concordate with Pope Pius VII, thus stopping defamations of clerics and making Trier a diocese.
In 1802, the Frenchman Charles Mannay became first bishop of the new founded diocese and, in 1803, the first Holy Mass since 1794 was celebrated in the Cathedral of Trier.
From 1840 on, the situation of Trier began to improve as the neighbouring state of Luxembourg, an important market for Trier-made products, joined the German Customs Union in 1842.
An important infrastructural improvement was the introduction of a shipping line operating with paddle-wheel steamers on the Moselle River, connecting Trier, Koblenz and Metz.
The people of Trier hoisted black-red-gold flags as democratic symbols, rang the church bells, organized a militia and took away the signs of Prussian rule.
In September 1944 during the Second World War, Trier was only a short distance from the frontline fighting and was subjected to almost daily bombardment by American artillery.
Two days later, on December 21 at 14:35, 94 Lancasters and 47 American fighter-bombers dropped 427 tonnes of ordnance (high-explosive, incendiary and napalm bombs).
The evolution of Trier as a university city took a further step forward with the opening on April 1, 1974, of the Martinskloster student residence halls.
[31] Other significant events of the 1970s include the discontinuation of the 99-year-old "Trierische Landeszeitung" newspaper on March 31, 1974, and the reopening of the restored Cathedral of Trier on May 1 of that same year.
During construction of an underground parking lot in October 1988, remnants of Roman fresco paintings were discovered beneath the Viehmarkt.
[33] A new discovery of Roman remains was made in April 2006, when traces of building walls were unearthed during demolition works in the city centre.
[35] At the beginning of the 4th century AD, Trier was the residence of the Roman Emperor and, with an estimated 80,000 inhabitants, the largest city north of the Alps.
This reorganisation in fact pushed the number of inhabitants beyond the 100,000 mark, which accorded the city of Trier Großstadt status.