The Roman History · Amm. 31.15.8

They seduced some picked soldiers of our army, who had revolted to them the day before, to pretend to escape back to their former comrades, and thus gain admittance within the walls; and after they had effected their entrance, they were secretly to set fire to some part of the city, so that the conflagration might serve as a secret signal, and while the garrison and citizens were occupied in extinguishing it, the walls might be left undefended, and so be easily stormed.

Ammianus Marcellinus · translated by C. D. Yonge · 1911 reprint
C. D. Yonge translation (preface dated February 1862); G. Bell and Sons, 1911; Project Gutenberg #28587
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