There have been mighty kings also over Jerusalem, which have ruled over all countries beyond the river; and toll, tribute, and custom, was paid unto them. Beyond the river - That is, the Euphrates. Both David and Solomon carried their conquests beyond this river. See 2 Samuel 8:3, etc., and 1 Kings 4:21, where it is said, Solomon reigned over all kingdoms from the river (Euphrates) unto the land of the Philistines; and unto the borders of Egypt.
Related Commentaries of Ezra 4:20
Ezra 4:20
20 There have been mighty kings also over Jerusalem, which have ruled over all countries beyond the river; and toll, tribute, and custom, was paid unto them.