Albert Barnes Commentary 2 Kings 14:13

"And Jehoash king of Israel took Amaziah king of Judah, the son of Jehoash the son of Ahaziah, at Beth-shemesh, and came to Jerusalem, and brake down the wall of Jerusalem from the gate of Ephraim unto the corner gate, four hundred cubits." — 2 Kings 14:13 (ASV)

The object of breaking down the wall was to leave Jerusalem at the mercy of her rival. It must have been among the conditions of the peace that the breach thus made should not be repaired.

Gates in Oriental cities are named for the places to which they lead. The gate of Ephraim must therefore have been a north gate, perhaps also known later as the “gate of Benjamin” (Jeremiah 37:13; Zechariah 14:10). The corner gate was probably a gate at the northwest angle of the city, where the north wall approached the Valley of Hinnom.

The entire breach was thus in the north wall, on the side where Jerusalem was naturally weakest. Josephus says that Joash drove his chariot through the breach into the town, a practice not unusual for conquerors.