Although this simple truth is sometimes overlooked, the primary concern of early medieval people, whose societies were agrarian, was the struggle to obtain food from the land. Agriculture was the single most important activity in virtually all European communities, even if how it was practiced varied widely from place to place. Thus, even communities like the Italian ones of the centuries after Rome's collapse, with their wealth of wild, uncultivated foodstuffs and endless resourcefulness at extracting products from uncultivated zones, confronted the problems of water management posed by their agriculture. The serfs on a manor in the Po's plain during the tenth century and urban horticulturalists in the sixth may have lived different lives, but as members of agrarian societies they shared concern for and interest in hydraulics. For throughout the Middle Ages, and indeed long thereafter, all Italian cultivation, planted or sown, annual or perennial, depended on the presence in the soil of the correct amount of water at the appropriate time.

When inclement weather tipped too much water onto the land, or when unseasonable drought sucked the fields and exploited wilderness dry, the prospects for everyone grew grim. In hopes of eluding the calamitous consequences for agrarian communities of too much or too little water, early medieval people developed two strategies. Either they adapted cultivation to the naturally occurring water, or they developed techniques of water control, designed to make it available where and when it was needed. Great landlords, peasants of various sorts, and horticulturalists all strove for a balanced, carefully dosed mixture of earth and water in tune with their ambitions.