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20th century. L. Sprague de Camp's writing career spanned from the 1930s to the 1990s, primarily during the 20th century. He published over 100 novels and short story collections, many of which were set in historical or science fiction worlds. His most famous works include the Conan the Barbarian series, co-written with Robert E. Howard, and the Lest Darkness Fall series, which explores the concept of time travel.