Liebfrauenkirche, Trier

The Diocese of Trier, in English historically also known as Treves ([tɾivz]) from French Trèves, is a Latin Church ecclesiastical territory or diocese of the Catholic church in Germany. When it was the archbishopric and Electorate of Trier, it was one of the most important states of the Holy Roman Empire, both as an ecclesiastical principality and as a diocese of the church. Unlike the other Rhenish dioceses—including Mainz and Cologne–Trier was the former Roman provincial capital of Augusta Treverorum. Given its status, Trier has continuously been an episcopal see since Roman times and is one of the oldest dioceses in all of Germany. The diocese was elevated to an archdiocese in the time of Charlemagne and was the metropolitan for the dioceses of Metz, Toul, and Verdun. After the victory of Napoleon Bonaparte of France, the archdiocese was lowered to a diocese and is now a suffragan in the ecclesiastical province of the Archdiocese of Cologne. The diocesan cathedral is the Cathedral of Saint Peter. The Cathedral Chapter retains the right to elect the bishop, rather than selection by papal appointment.

The High Cathedral of Saint Peter in Trier (German: Hohe Domkirche St. Peter zu Trier), or Trier Cathedral (German: Trierer Dom), is a Roman Catholic cathedral in Trier, Rhineland-Palatinate, Germany. It is the oldest church in Germany and the largest religious structure in Trier, notable for its long life span and grand design. The central part of the nave was built of Roman brick in the early fourth century, resulting in a cathedral that was added onto gradually in different eras. The imposing Romanesque westwork, with four towers and an additional apse, has been copied repeatedly. The Trier Cathedral Treasury contains an important collection of Christian art. In 1986 the church was listed as a UNESCO World Heritage Site, as part of the Roman Monuments, Cathedral of St. Peter and Church of Our Lady in Trier.

Trier ( TREER, German: [tʁiːɐ̯] ; Luxembourgish: Tréier [ˈtʀəɪɐ] ), formerly and traditionally known in English as Trèves ( TREV, French: [tʁɛv]) and Triers (see also names in other languages), is a city on the banks of the Moselle in Germany. It lies in a valley between low vine-covered hills of red sandstone in the west of the state of Rhineland-Palatinate, near the border with Luxembourg and within the important Moselle wine region. Founded by the Celts in the late 4th century BC as Treuorum and conquered 300 years later by the Romans, who renamed it Augusta Treverorum ("The City of Augustus among the Treveri"), Trier is considered Germany's oldest city. It is also the oldest seat of a bishop north of the Alps. Trier was one of the four capitals of the Roman Empire during the Tetrarchy period in the late 3rd and early 4th centuries. In the Middle Ages, the archbishop-elector of Trier was an important prince of the Church who controlled land from the French border to the Rhine. The archbishop-elector of Trier also had great significance as one of the seven electors of the Holy Roman Empire. Because of its significance during the Roman and Holy Roman empires, several monuments and cathedrals within Trier are listed as a UNESCO World Heritage Site.With an approximate population of 110,000, Trier is the fourth-largest city in its state, after Mainz, Ludwigshafen, and Koblenz. The nearest major cities are Luxembourg City (50 km or 31 mi to the southwest), Saarbrücken (80 kilometres or 50 miles southeast), and Koblenz (100 km or 62 mi northeast). The University of Trier, the administration of the Trier-Saarburg district and the seat of the ADD (Aufsichts- und Dienstleistungsdirektion), which until 1999 was the borough authority of Trier, and the Academy of European Law (ERA) are all based in Trier. It is one of the five "central places" of the state of Rhineland-Palatinate. Along with Luxembourg, Metz and Saarbrücken, fellow constituent members of the QuattroPole union of cities, it is central to the greater region encompassing Saar-Lor-Lux (Saarland, Lorraine and Luxembourg), Rhineland-Palatinate, and Wallonia.

St. Gangolf's Church is a Roman Catholic church in Trier, Germany. It is dedicated to St. Gangulphus. After Trier Cathedral, it is the second oldest church building in the city.

The Aula Palatina, also called Basilica of Constantine (German: Konstantinbasilika), at Trier, Germany, is a Roman palace basilica and an early Christian structure built between AD 300 and 310 during the reigns of Constantius Chlorus and Constantine the Great.Today it is used as the Church of the Redeemer and owned by a congregation within the Evangelical Church in the Rhineland. The basilica contains the largest extant hall from antiquity (see List of ancient Greek and Roman roofs. The hall has a length of 67 m, a width of 26.05 m and a height of 33 m. Because of its testimony to the imperial importance of Trier during the Roman Empire and its architecture, the Aula Palatina was designated as a UNESCO World Heritage Site in 1986 as part of the Roman Monuments, Cathedral of St. Peter and Church of Our Lady in Trier site.

The Electoral Palace (German: Kurfürstliches Palais) in Trier, Germany, was the residence of the Archbishops and Electors of Trier from the 16th century until the late 18th century. It now houses various offices of the federal government and often hosts classical music concerts.

The St. Simeon’s Collegiate Church [German: Simeonstift] was a collegiate church in Trier, Germany, near the Roman city gate of the Porta Nigra [Latin, “Black Gate”]. Named after the Greek monk, St. Simeon of Trier, it is now a city museum in the former collegiate church’s buildings under the name, Stadtmuseum Simeonstift [City Museum of the Simeonstift]. The church was created in 1037. In 1028 Simeon of Trier settled at the Porta Nigra as a hermit. He was supposed to have walled himself up there at the gate’s east tower. After his death on 1 June 1035, he was buried in his room on the ground floor. In the same year, probably for Christmas, he was canonized by Pope Benedict IX, in one of the first canonizations ever made by a Pope. In honor of the new saint, they built the Simeonstift and converted the former tower to a Doppelkirche [German, “twin church”]. The Archbishop of Trier at that time, Poppo von Babenberg, personally had known the hermit and travelled with him. But a certificate of incorporation of the Simeonstift could not be obtained from him and it was probably never given. However, recent research showed that the church was founded soon after the canonization of Simeon. The Simeonstift was a two-story cloister in four wings with a dormitory in the north wing and a refectory in the west wing. According to the dendrochronological findings, the north wing dates from 1040. The first reliable documentation is a document of 1048, which proves the existence of a provost’s office and therefore the existence of a collegiate church’s charter. Emperor Henry IV in 1098 confirmed all his possessions to the Simeonstift and granted, namely, more than sixty properties and privileges to it.The doppelkirche conversion of the Porta Nigra was reversed more than 750 years later, in 1804, by the order of Napoleon. Since then, the city gate has reverted almost to its original Gallo-Roman condition. Only the Romanesque east side of the choir still testifies from the outside to the fact that the Porta Nigra was once an imposing church.

The Porta Nigra (Latin for black gate), referred to by locals as Porta, is a large Roman city gate in Trier, Germany. It is a UNESCO World Heritage Site.The name Porta Nigra originated in the Middle Ages due to the darkened colour of its stone; the original Roman name has not been preserved.

The Rheinische Landesmuseum Trier is an archaeological museum in Trier, Germany. The collection stretches from prehistory through the Roman period, the Middle Ages to the Baroque era with a strong emphasis on the Roman past of Augusta Treverorum, Germany's oldest city. Its collections of (local) Roman sculptures, Roman mosaics and frescos are among the best in Germany (along with those of the Römisch-Germanisches Museum in Cologne, the Rheinisches Landesmuseum Bonn and the Römisch-Germanisches Zentralmuseum in Mainz).

The Trier Imperial Baths (German: Kaiserthermen) are a large Roman bath complex in Trier, Germany. The complex was constructed in the early 4th century AD, during the reign of Constantine I. During that time, Trier was a major imperial hub, being a primary residence for Constantine's son Crispus. The baths were built around hot water pools reaching 40°C. Underneath the complex was a network of underground passageways used by the staff which can still be seen today, along with the remains of the sewer system. However, the baths were never completed and were made into a castle in the Middle Ages.

The Karl Marx House museum (German: Karl-Marx-Haus) is a biographical and writer's house museum in Trier (Rhineland-Palatinate, Germany). In 1818, Karl Marx, the father of Marxism, which influenced both modern socialism and communism, was born in the house. It is now a museum about Karl Marx's life and writings as well as the history of communism.

Trier Hauptbahnhof is a railway station for the city of Trier, in the German state of Rhineland-Palatinate. It is a through station, about 500 metres (550 yd) east of the inner city and the Porta Nigra.