When did western cities become the engines of creativity modern theorists envision them to be? We approach this issue by investigating how much elite authors benefited from agglomerating in early modern London. Building a new panel dataset documenting the place of residence and annual publications of 2,026 prolific authors over the period 1482-1800, we conduct longitudinal author-level analyses. Our results suggest agglomeration benefits in London's knowledge economy reached levels comparable to those documented in modern cities by the late 16th century. Exploring mechanisms, we find that moving to London improved opportunities for collaboration and, relatedly, the quality of books produced. We find similar agglomeration economies (and mechanisms) in the towns leading Britain's industrial revolution in the 18th century (but not before).