This paper provides a new proxy for preindustrial economic activity by combining records from the world’s largest library collections with historical Islamic biographies. A two-pronged statistical framework exploits variation in the number of authors affiliated with a city to derive a high-frequency measure of economic development, improve existing city growth estimates and generate preliminary growth estimates where none exist. To illustrate how the data allow for economic analysis by year instead of century, the paper revisits growth during the rise of the Atlantic trade and documents the enduring impact of the Mongol invasions.