E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Those held by the Romans only once in a century. While the kings reigned they were held in the Campus Martius, in honour of Pluto and Proserpine, and were instituted in obedience to the Sibylline verses, with the promise that the empire should remain in safety so long as this admonition was observed.