German art historian known in particular for his large inventory of monuments in the Rhineland area, many of which were destroyed or severely damaged in World War II.
Clemen’s earliest publications on medieval art impressed the authorities of the province enough to make him responsible for the inventory of its monuments. He began, in 1891, the publication of the series Die Kunstdenkmäler der Rheinprovinz (Monuments of the Rhine Province), for which he served as editor for the next 46 years. The project culminated in 1937 with the publication of the volume on the Cologne Cathedral, Der Dom zu Köln, a collaboration with Heinrich Neu and Fritz Witte, but with Clemen as main author.
During World War I, Clemen was head of the art commission for the German occupation force in Belgium. His work during the war years resulted both in a book on the subject, Kunstschutz im Kriege (in English translation as Protection of Art During the War, both 1919) and in the two-volume Belgische Kunstdenkmäler (Munich, 1923).
Many of the monuments Clemen had dedicated himself to protect, including several of the medieval churches in Cologne, were destroyed during World War II, and his house was destroyed by air bombardment in 1944, along with his library and a manuscript for a large treatment of the history of the art of the Rhineland.
He died on 8 July 1947 in Endorf.
Link to Wikipedia biography