At its peak in the second century, the Roman Empire dominated nearly two million square miles of the world. As with most such grand achievements, it couldn’t have happened without the development of certain technologies. The long reach of the Eternal City was made possible in large part by the humble technology of the road — or at least it looks like a humble technology here in the twenty-first century.

Roads existed before the Roman Empire, of course, but the Romans built them to new standards of length, capacity, and durability. How they did it so gets explained in this video. On a representative stretch of Roman-road-to be, says the narrator, a “wide area would be deforested.” Then “the topsoil would be removed until a solid base was found.” Atop that base, workers laid down curbs at the width determined by the road plan, then filled the gap between them with a foundation of large stones.