The occupying army had ordered striking professors at the University of Ghent to continue teaching. What is known is that Pirenne was questioned by German occupiers on 18 March 1916, and subsequently arrested. How involved Pirenne was in the Belgian resistance during World War I is not known. In 1914, Belgium was invaded by the German Empire and placed under German military occupation. The Maison Vivroux in Verviers where Pirenne was born in 1862 Pirenne was a close friend of German historian Karl Lamprecht (1856–1915), until they broke during the war when Lamprecht headed a mission to invite Belgians to collaborate with Germany's long-term goals. He was Rector of the University of Ghent from 1918 to 1921. After World War I he was the most prominent and influential historian in Belgium, receiving numerous honors and committee assignments. He became Professor of History at the University of Ghent in 1886, a post he held until the end of his teaching career in 1930. He studied at the University of Liège where he was a student of Godefroid Kurth (1847–1916).

Pirenne was born in Verviers, an industrial city in the Province of Liège in south-east Belgium. Though Pirenne had his opponents, notably Alfons Dopsch who disagreed on essential points, several recent historians of the Middle Ages have taken Pirenne's main theses, however much they are modified, as starting points. Pirenne argued that profound social, economic, cultural, and religious movements in the long term resulted from equally profound underlying causes, and this attitude influenced Marc Bloch and the outlook of the French Annales School of social history. Henri Pirenne's reputation today rests on three contributions to European history: for what has become known as the Pirenne Thesis, concerning origins of the Middle Ages in reactive state formation and shifts in trade for a distinctive view of Belgium's medieval history and for his model of the development of the medieval city. He also became prominent in the nonviolent resistance to the Germans who occupied Belgium in World War I. Pirenne made a lasting contribution to the study of cities that was a controversial interpretation of the end of Roman civilization and the rebirth of medieval urban culture. A medievalist of Walloon descent, he wrote a multivolume history of Belgium in French and became a prominent public intellectual. Henri Pirenne ( French: 23 December 1862 – 24 October 1935) was a Belgian historian. Medieval Cities: Their Origins and the Revival of Trade (1927) Medieval history, economic history, Belgian history

Henri pirenne books