Ammianus Marcellinus Res Gestae 18.5.3

[3] And to the end that he might elude the sentinels, he bought at no great price a farm in Iaspis, a place washed by the waters of the Tigris. And since because of this device no one ventured to ask one who was now a landholder with many attendants his reason for coming to the utmost frontier of the Roman empire, through friends who were loyal and skilled in swimming he held many secret conferences with Tamsapor, then acting as governor of all the lands across the river, whom he already knew; and when active men had been sent to his aid from the Persian camp, he embarked in fishing boats and ferried over all his beloved household in the dead of night, like Zopyrus, that famous betrayer of Babylon, but with the opposite intention. ¹