E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A narrow pass in the mountains near Capua, now called the Valley of Arpaia. It was here that the Roman army, under the consuls T. Veturius Calvinus and Sp. Postumius fell into the hands of the Samnites, and were made to pass under the yoke.
Hard as it was to abandon an enterprise so very dear to him . he did not hesitate to take the more prudent course of passing under (sic) the Caudine Forks of the Monroe doctrine, and leave Maximilian and the French bondholders to their fate.Standard, Nov. 17th, 1866.