This article reconsiders Schlieffen's Cannae ideal and offers an historical perspective on the question of its applicability. Concurring with Hans Delbrück's interpretation, Schlieffen understood that the battle of Cannae was decided by a cavalry attack on the rear of the Roman phalanx. This model had no influence on the Schlieffen plan of 1905, which reflects a quite different method of envelopment taught by Schlieffen before he adopted the Cannae paradigm in 1909. Cannae was in any case a problematic exemplar, given that modern firepower severely limited the scope of cavalry operations. But if the Cannae programme was untimely in Schlieffen's own time, it also prefigured a rebirth of the cavalry idea in the age of mechanized warfare.