Sometime in the later 1590s Justus Lipsius and one of his Louvain students had a nice conversation about sewers. The student thought the topic comic and stifled a giggle, but Lipsius soon set him straight. The sewers of ancient Rome had been as physically imposing as any other great Roman artifact. Moreover—and more important to the student of history—they were directly linked with the other artifacts and institutions that had provided the material basis for Rome's uniquely splendid civilization, with its powerful armies, Stoic philosophy, and inimitable literature. Only a full study of the material life of ancient Rome could explain the continuous population growth that had enabled the city to expand so far and last so long. The two of them were off, happily embarked on a long inquiry into the secret and public means that Rome had used to enlarge its population, encourage trade, and avoid corruption over the many centuries between Romulus and the Antonines (Lipsius, 161-63).