The Basilica of Saint-Pierre-Aux-Nonnains is one of the oldest Christian churches in the world still standing. Erected sometime in the 4th century AD, it was originally part of a Roman-era spa when Divodurum, the former name of Metz, was a major military and trade center along the Germanic frontier. Specifically it was used as a pagan gymnasium when Christianity in Western Europe was still in its infancy. It was one of the few buildings in the city to remain standing after the Huns passed through in 451 AD.
Metz was an important cradle of Frankish civilization, with both Merovingians and Carolingians tracing their ancestry to the place. After the conversion of Clovis I to Catholicism, Metz became a Christian stronghold. During the 7th century, the old Roman gymnasium was converted to use as a Benedictine church. During the reign of Charlemagne, Metz was almost chosen as the capital city of the newly founded Holy Roman Empire, an honor which was instead bestowed on nearby Aachen. Neverthless Charlemagne was apparently fond of the old church, and two of his sons were buried in what would later be designated the Basilica of Saint-Pierre-Aux-Nonnains.
Amazingly, the original Roman structure remained essentially intact throughout the Middle Ages. Apparently by the 16th century the old edifice was showing its age, and the Church moved out. It then spent over 400 years in service as a warehouse: a perfectly intact thousand-year-old building, one of the best preserved Roman constructions in the world, was then used for storage. Thankfully, its historical importance was recognized in the 1970s and the basilica was restored. It is now used primarily as a concert hall, a fitting tribute to its medieval musical heritage.
The interior is much less Roman in appearance than the exterior, as the whole place was renovated in the 10th century, and again in the 20th century. Although still designated as a Basilica by the Roman Catholic Church, the building’s use nowadays is for musical functions and exhibitions. It is certainly an ideal place to see Gregorian Chant music performed.
References:The Clementinum is a historic complex of buildings in Prague. Until recently the complex hosted the National, University and Technical libraries, the City Library also being located nearby on Mariánské Náměstí. The Technical library and the Municipal library have moved to the Prague National Technical Library at Technická 6 since 2009. It is currently in use as the National Library of the Czech Republic.
Its history dates from the existence of a chapel dedicated to Saint Clement in the 11th century. A Dominican monastery was founded in the medieval period, which was transformed in 1556 to a Jesuit college. In 1622 the Jesuits transferred the library of Charles University to the Klementinum, and the college was merged with the University in 1654. The Jesuits remained until 1773, when the Klementinum was established as an observatory, library, and university by the Empress Maria Theresa of Austria.