The Roman History · Amm. 23.2.2

He only warned Arsaces, king of Armenia, to collect a strong force, and wait for his orders, as he should soon know which way to march, and what to do. Then, as soon as prudence afforded him an opportunity, hastening to anticipate every rumour of his approach by the occupation of the enemy's country, before spring had well set in, he sent the signal for the advance to all his troops, commanding them to cross the Euphrates.

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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