'River' in the Bible

Further, I said to the king, If it is the king's pleasure, let letters be given to me for the rulers across the river, so that they may let me go through till I come to Judah;

Then I came to the rulers of the lands across the river and gave them the king's letters. Now the king had sent with me captains of the army and horsemen.

By their side were working Melatiah the Gibeonite and Jadon the Meronothite, the men of Gibeon and of Mizpah from the seat of the ruler across the river.