First published between 1880 and 1885, Joseph B. Mayor's three-volume edition of De Natura Deorum places Cicero's speculative theological dialogue in the context of the arguments of the Epicureans, the Stoics, the Academics, and their predecessors. This volume presents Cicero's Book 3, which takes up questions of Roman divination, worship, and mythology and ponders the relationship of philosophy to superstition. Is it possible, as Mayor asks, to 'unite reason and religion'? With this provocative question at its heart, the last book of Cicero's theological debate demonstrates its author's wit and imagination, as he evaluates not just the divisions among the Roman philosophical schools but the very grounds of divine existence. Containing a detailed textual commentary, a collation of manuscripts, and a substantial introduction to the three volumes as a whole, Mayor's book is still valuable today as a clear presentation of Cicero's complex philosophical project.