De Re Rustica (Res Rusticae)

Written when Varro was eighty years old, this three-book dialogue on agriculture, animal husbandry, and small-livestock farming is the most complete of his roughly seventy works to survive intact, most of the rest of his vast scholarly output being lost. Cast as conversations among Roman gentleman-farmers, the work systematizes practical agricultural knowledge, crop rotation, soil types, livestock breeding, into an organized technical manual meant for the senatorial class that increasingly managed estates through slave labor rather than direct cultivation. Its influence stretched through Columella's later, more comprehensive treatise and into medieval and Renaissance farming manuals that drew on Varro as the standard ancient authority.