Isaiah 17: 3-4. “The fortress also shall cease from Ephraim, ad the kingdom from Damascus, and the remnant of Syria: they shall be as the glory of the children of Israel, saith the Lord of hosts. And in that day it shall come to pass, that the glory of Jacob shall be made thin, and the fatness of his flesh shall wax lean.”
The fortress – The strong place of defense; the fortified place, will be destroyed. Ephraim was the name given to the kingdom of Israel, the ten northern tribes, because Ephraim was the largest and was a leading tribe in their councils. They were confederate with Damascus in Syria, against Judah.
The remnant that would be left of the kingdom of Syria after Damascus was destroyed would be like the “glory of the children of Israel,” meaning that the fortified towns and fortresses of the kingdom of Israel would be destroyed, and so it would be for Damascus, because they were allies.