דברי הימים ב, פרק ט׳, פסוק כ״ו

During the reign of Solomon, the kingdom reached the peak of its size, taking in many nations and states. Solomon held authority over all the surrounding kings, and his rule covered a vast area, stretching from almost the entire region of Syria down to the southern parts of the land [ביאור שטיינזלץ].

The borders of this great empire were clearly established, with the eastern boundary marked by the Euphrates River. The historical record in the Book of Chronicles specifically clarifies the parallel account in the Book of Kings by explicitly identifying this river as the Euphrates [מלבי"ם]. Recognized as the river flowing out of the Garden of Eden, it served as the starting point of the East and formed the strict eastern edge of Solomon's territory [מצודת דוד]. From that eastern boundary, the empire spread outward to its western and southern limits. It reached the land of the Philistines and covered the entire southern area right up to the border of Egypt [ביאור שטיינזלץ].