The Spanish Empire was an improbable creation. Relatively poor, meagrely populated and only recently integrated, Spain nonetheless built the largest realm the world had seen. From a landlocked capital, the Spanish created an empire on four continents, its reach in America alone spreading from the upper Missouri to Tierra del Fuego.

In How the Spanish Empire was Built, Felipe Fernández-Armesto and Manuel Lucena Giraldo demonstrate how this unlikely venture grew and was maintained thanks to engineers. In accordance with early modern parlance, the authors use the term ‘engineer’ to cover a range of occupations, such as master craftsman and specialist artisan.

Often the engineers doubled as soldiers or churchmen. They designed and built roads, waterways and mines in Asia, Africa and America. They managed settlements and communications in mountains, plains, forests and deserts and erected the fortifications needed to defend an overstretched empire.

At the frontier of the sprawling territory were the Spanish missions. The mission system enabled the crown to extend its dominion, especially to remote, topographically challenging regions that lay beyond military reach. Missionaries designed and built everything from mills to bridges and were, in the authors’ words, the ‘engineers of