While it was clear from the start that the wall was of Roman origin, it was initially believed to be the ruins of a public assembly room. But what stumped experts were "unusual, niche-like divisions" in the wall, says Cologne historic preservation official Marcus Trier.
After comparing the structure with other ancient buildings, including the Roman city of Ephesus in present-day Turkey that had a monumental library, it turned out that the remains in Cologne belonged to a library built in the 2nd century in the then-Roman city.
Stuttgart's municipal library
Designed to be an intellectual and cultural center, the new Stuttgart municipal library was built in 2011, a towering nine-story cube. Outside, it's constructed of pale grey concrete framing glass bricks. Inside, it's stark white. Books that line the walls of the light-flooded five-story gallery hall are the only splashes of color. At night, the library is illuminated in different colors.
Duchess Anna Amalia library
The Duchess Anna Amalia Library is a small gem in Weimar that houses books, maps, musical scripts and ancestral registers. It's named after the duchess who saw to it that the court's book collection was moved into the Rococo library in 1766. A fire in 2004 destroyed part of the precious collection. After undergoing restoration, the UNESCO-listed building reopened three years later.
Herzog August Library
Bibliotheca Augusta, the Herzog August Library in Wolfenbüttel, is one of the oldest libraries in the world that has made it to the present day without losses to its famous collections. An avid book collector, Duke August (1579-1666) made it one of the largest European libraries of his day. Scholars continue to turn to the library for its wealth of medieval literature.
Due to its cranial shape, this library in Berlin has been dubbed "The Brain." It houses the libraries for the philosophy and humanities departments at the capital's Freie Universität and has quickly become an architectural landmark. It was designed by internationally renowned architect Norman Foster and opened in 2005.
Oberlausitz Library of Sciences
The Oberlausitz Library of Sciences in Görlitz, right on the border with Poland, dates back to 1806. Plain but inviting, it is one of the most striking early classicist library halls. More than 140,000 books document the history, culture, nature and society of the region between Dresden to the West and Wroclaw to the East.
Jacob and Wilhelm Grimm Center
The spectacular Grimm Center is a part of Berlin's Humboldt University. Built in 2009, it houses a library and the university's computer and media services. The reading room, above, is at the heart of the building. It gives people "a sense of the outdoors" through its size and tiered, almost scenic design, says architect Max Dudler. It offers "the feeling of reading under the open sky."
Bavarian State Library
Collections begun in the mid 16th century have grown to more 10 million books in the Bavarian State Library in Munich, once known as the Bibliotheca Regia Monacensis. The collections found a home in the current building between 1832 and 1843, which was almost completely destroyed during World War II. The library took years to rebuild.
Kolumba reading room
Granted, it's nothing like the other libraries in this selection, but the Kolumba Museum's reading room is a gem in its own right. It's a space made for contemplation with a stunning view of downtown Cologne from tall windows, the walls paneled in grained wood. The books? Exhibition catalogues, individual publications and a changing array of novels, children's and art books chosen by museum staff.
The original building was probably two stories tall, with a size of around 20 by 9 meters — an extension was later added. Scholars and researchers would have enjoyed a lot of choice, Trier says, with "certainly several thousand scrolls to borrow."
The remains of the ancient library are to be integrated into the new church building, with part of the wall being made accessible to visitors. Other parts of the excavation will be preserved to give access to future generations of archaeologists.
The western German city on the Rhine River is known worldwide for its magnificent Gothic cathedral; however Cologne is also rich in Roman history.
A Roman general established an urban settlement called Ara Ubiorum in the Cologne area in 38 BC. The military outpost flourished and was given colony status by Emperor Claudius several decades later.
Claudius renamed it Colonia Claudia Ara Agrippinensium, or CCAA for short, after his wife Agrippina the Younger who was born there.
From walls, city gates and aqueducts above ground, to delicate mosaics and historic sewer canals below ground, a newly found library is set to become a significant part of Cologne's, and Germany's, ancient Roman heritage.
The Duchess Anna Amalia Library in Weimar got its present name in 1991. It had previously been called simply the "Herzogliche Bibliothek" ("The Ducal Library") for 300 years. The building with its famous rococo hall (above) was partially destroyed in a fire, but it reopened on October 24, 2007.
A football field or a library?
Don't worry if you don't have a student card, the library of the University of Technology in Delft, the Netherlands is worth of visiting even without it. The sloping, grass-grown top of the building is particularly striking, and the 42-metre-high cone that pierces the building in the middle hides four floors full of books.
Tulipwood and ebony
British newspaper "The Daily Telegraph" included the Biblioteca Joanina in Coimbra, Portugal in the 2013 list of the most spectacular libraries in the world. It bears the name of the Portuguese king John V, who commissioned its construction. All bookshelves are made of tulipwood and ebony, and the place is now part of the Faculty of Law.
The ancient world meets modernity
The Library of Alexandria was the most famous library in the world before it was destroyed in flames about 2,000 years ago. It is said to have contained the whole knowledge of the then world on about 490,000 papyrus rolls. The new library of Alexandria, which continues the tradition, opened in 2002. Its final cost? More than 220 million dollars (€187 m.).
Some of the specimens in possession of the Abbey library of Saint Gall in St. Gallen, Switzerland are over 1,300 years old, and visitors can see the monastery plan, the oldest building plan in Europe, or an Egyptian mummy. The Büchersaal ("The Book Hall," above) has been on the UNESCO World Heritage list since 1983.
Rescued by a president
Pay a visit to the Library of Congress whenever you are in Washington, D. C. The library was founded in 1800 but was burnt down by the British just 14 years later. Thomas Jefferson, the third President of the United States, sold about 6,500 books from his private collection to fund the $24,000 restoration. The main reading room pictured above was built in the Neo-Renaissance style.
An oak-ey idea
The double-storey "Long Room" in the old Trinity College Library in Dublin is 64 meters long and 12 meters wide. But the space wasn't always as impressive as it is today. Its flat, plaster ceiling was removed in 1858 and substituted by a new roof made of oak.
Everything is big in China
With an archive of more than 30 million books and other media, the National Library of China is one of the seven largest libraries in the world. It was built as the "Capital Library" in 1809 and later renamed the "Beijing Library" in 1928 after the People's Republic of China was established. Its current name was approved by the state in 1998.