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An army marches on its stomach.

Attributed in Wash. Post, 18 Sept. 1898. According to the Oxford Dictionary of Quotations, this was "probably condensed from a long passage in E. A. de Las Cases Memorial de Ste-Helene (1823) vol. 4, 14 Nov. 1816; also attributed to Frederick the Great, in Notes and Queries 10 March 1866." The 1866 attribution to Frederick is worded "an army moves on (or by) its stomach."
An army marches on its stomach.