The university opened on 8 November 1834 in Mechelen, not Leuven, under the rectorship of a young priest and historian named Pierre de Ram. Pope Gregory XVI had authorized the founding with a papal brief the previous December. The Belgian bishops, anxious to plant a confessional Catholic university in the still-new kingdom of Belgium, had moved quickly - and politically. The announcement set off demonstrations in Ghent, Leuven, and Liege, in part because Belgian liberals saw the new university as a Trojan horse. They had a point. Within thirteen months the bishops had moved the institution to Leuven itself and renamed it the Catholic University of Leuven - implying, although Belgian courts would later flatly deny it, that this was the lawful successor of the Old University of Leuven that the French Republic had closed in 1797. Belgian liberals, furious, founded the secular Free University of Brussels in response. The Catholic university kept the name anyway. It still does, more or less - the courts ruled three times, in 1844, 1855, and 1861, that the claim of continuity was legally false. The institution simply continued to make the claim unofficially. By the time anyone noticed the courts had stopped paying attention, the new university was beginning to produce some of the most consequential scholars in Europe.

On 25 August 1914, three weeks into the First World War, German troops set fire to the city of Leuven. They burned about half of it, including the old University Hall on Naamsestraat, parts of which dated to 1317. The university library went with it - 230,000 books, 950 manuscripts, 800 incunabula. Among the losses were one of the oldest known Czech Bibles and the only Easter Island rongorongo tablet then preserved in Europe. The destruction became, by accident, one of the great propaganda images of the war. American newspapers ran photographs of the burning university for weeks; private donations to rebuild it arrived from around the world. The American architect Whitney Warren, who had designed Grand Central Terminal, was commissioned to build a replacement. His neo-Flemish-Renaissance library opened in 1928, paid for largely with American money and topped with a 48-bell carillon dedicated to American engineers who had died in war. Then, in May 1940, German troops returned. The Warren library burned. The collection that had been painstakingly rebuilt over twenty-two years - now around 900,000 manuscripts and books - was destroyed a second time. After 1945 the building was rebuilt according to Warren's original plans. The carillon, neglected for decades, was finally restored in 1983 with help from the Belgian American Educational Foundation. Ronald Reagan sent a statement to the rededication. The bells are still there.

For a university repeatedly destroyed, its alumni list is astonishing. Theodor Schwann, a professor in the early years, developed cell theory. Georges Lemaitre, a Belgian astronomer-priest who took his doctorate at Leuven in 1920, proposed the Big Bang theory before Edwin Hubble had finished interpreting his telescope data. Christian de Duve, another Leuven biologist, shared the 1974 Nobel Prize for Physiology or Medicine for discoveries about the inner organization of the cell. The Belgian-American Albert Claude shared that same Nobel; he had also studied at Leuven. The university produced a Prime Minister of Belgium who won the Nobel Peace Prize (Auguste Beernaert, 1909), a Dominican friar who won it for refugee work after the Second World War (Dominique Pire, 1958), the heir to the throne of Austria-Hungary (Otto von Habsburg), the founder of liberation theology (Gustavo Gutierrez), and a Pakistani metallurgist who would become the father of his country's nuclear weapons program (A. Q. Khan). The Chinese geographer Weng Wenhao, the Lithuanian poet Antanas Baranauskas, the first African-American Catholic priest with a doctorate (Patrick Francis Healy of Georgetown), and Herman Van Rompuy, the first President of the European Council - all of them passed through Leuven. So did Hendrik Elias and Leon Degrelle, two of the most notorious Belgian Nazi collaborators, who turned the same education to very different ends.

From its founding in 1834 the university lectured in French. Latin still appeared in theology, but the language of instruction, administration, and social life was French - even though Leuven itself was, and had always been, a Dutch-speaking Flemish town. Dutch-language courses began only in 1930. Flemish nationalism had been building since the late 19th century, and the university's continued reliance on French became a wound that never quite healed. In 1962, constitutional reforms made the two language sections autonomous within a common governance structure. This satisfied no one. Tensions exploded in early 1968 when a French-speaking professor proposed on television that Leuven be absorbed into a Greater Brussels bilingual zone. Flemish students poured into the streets chanting Leuven Vlaams, Walen Buiten - Leuven Flemish, Walloons Out. The demonstrations escalated for weeks. In February 1968 the Belgian government collapsed because it could not resolve the question. In June, the bishops capitulated. The university would split. The Dutch-language half would remain in Leuven and become the Katholieke Universiteit Leuven, KU Leuven. The French-language half would move thirty kilometers south to a brand-new town built from scratch on farmland - Louvain-la-Neuve, New Leuven - and become the Universite catholique de Louvain. The library's four million books were divided by alternating shelfmark. The rancor lasted decades.

Today the two universities cooperate. Joint research centers exist. Doctoral students cross between them. But the geography of the split remains visible. Louvain-la-Neuve is a planned town of about 25,000, half of whom are students. Leuven is a medieval city of about 100,000 dominated by a much larger university. KU Leuven now ranks consistently among the top fifty universities in the world. UCLouvain is the largest French-speaking university in Belgium. Neither would say the split was a tragedy in retrospect; both would probably say it was the price of holding the country together. The original 1834 institution does not technically exist anymore. But the library on the Ladeuzeplein still has its carillon, the Big Bang still has a Leuven address on its birth certificate, and the words painted on Leuven walls in the spring of 1968 - Leuven Vlaams - still describe, in the most literal way, the city you walk through today.