'River' in the Bible

I also said to the king: “If it pleases the king, let me have letters written to the governors of the region west of the Euphrates River, so that they will grant me safe passage until I reach Judah.

Next to them the repairs were done by Melatiah the Gibeonite, Jadon the Meronothite, and the men of Gibeon and Mizpah, who were under the authority of the governor of the region west of the Euphrates River.