1. Henri 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 was born in Verviers, an industrial city in the Province of Liege in south-east Belgium.
Henri Pirenne studied at the University of Liege where he was a student of Godefroid Kurth.
Henri Pirenne became Professor of History at the University of Ghent in 1886, a post he held until the end of his teaching career in 1930.
Henri Pirenne was Rector of the University of Ghent from 1918 to 1921.
Henri Pirenne was a close friend of German historian Karl Lamprecht, until they broke during the war when Lamprecht headed a mission to invite Belgians to collaborate with Germany's long-term goals.
How involved Henri Pirenne was in the Belgian resistance during World War I is not known.
The German officer questioning Henri Pirenne asked why he insisted on answering in French when it was known that Henri Pirenne spoke excellent German and had done postgraduate studies at Leipzig and Berlin.
Henri Pirenne responded: "I have forgotten German since 3 August 1914", the date of the German invasion of Belgium, part of Germany's war plan to defeat France.
Henri Pirenne was held in Crefeld, then in Holzminden, and finally in Jena, where he was interned from 24 August 1916 until the end of the war.
Henri Pirenne was denied books, but he learned Russian from soldiers captured on the Eastern Front and subsequently read Russian-language histories made available to him by Russian prisoners.
Henri Pirenne attacked race theory and Volkisch nationalism as the underlying causes of German wartime excesses.
Henri Pirenne edited the work by inserting dates for which his father was uncertain in parentheses.
In brief, the Henri Pirenne Thesis, an early essay in economic history diverging from the narrative history of the 19th century, notes that in the ninth century long-distance trading was at a low ebb; the only settlements that were not purely agricultural were the ecclesiastical, military and administrative centres that served the feudal ruling classes as fortresses, episcopal seats, abbeys and occasional royal residences of the peripatetic palatium.
Henri Pirenne's thesis takes as axiomatic that the natural interests of the feudal nobility and of the urban patriciate, which came to well-attested frictions in the thirteenth and fourteenth centuries, were in their origins incompatible.
Henri Pirenne postponed the demise of classical civilization to the 8th century.
Henri Pirenne challenged the notion that Germanic barbarians had caused the Western Roman Empire to end and he challenged the notion that the end of the Western Roman Empire should be equated with the end of the office of emperor in Europe, which occurred in 476.
Henri Pirenne pointed out the essential continuity of the economy of the Roman Mediterranean even after the barbarian invasions, and that the Roman way of doing things did not fundamentally change in the time immediately after the "fall" of Rome.
Henri Pirenne used statistical data regarding money in support of his thesis.
Henri Pirenne's thesis did not convince most of the historians at the time of its publication, but historians since that time generally agree it has stimulated debate on the Early Middle Ages, and has provided a provocative example of how periodization would work.
The unity of the country might appear accidental, something which Henri Pirenne sought to disprove in his History of Belgium by tracing Belgium's history back to the Roman period.
Henri Pirenne's ideas, promoting a form of Belgian nationalism, have proved controversial.
Henri Pirenne's history cemented his reputation as one of Belgium's leading public intellectuals in his lifetime.
Henri Pirenne's thesis remains crucial to the understanding of Belgium's past, but his notion of a continuity of Belgian civilization forming the basis of political unity has lost favour.
Henri Pirenne donated the majority of his personal library to the Academia Belgica in Rome.
Henri Pirenne was the author of Medieval Cities: Their Origins and the Revival of Trade, a book based on lectures he delivered in the United States in 1922.
Henri Pirenne argued that capitalism originated in Europe's cities, as did democracy.
Pirenne wrote a two-volume A History of Europe: From the End of the Roman World in the West to the Beginnings of the Western States, a remarkable but incomplete work which Pirenne wrote while imprisoned in Germany during World War I It was published by his son in 1936.