cities of the south - namely, south of Judea; farthest off from the enemy, who advanced from the north.
shut up - that is, deserted (Isa 24:10); so that none shall be left to open the gates to travelers and merchants again [Henderson]. Rather, shut up so closely by Nebuchadnezzar’s forces, sent on before (2Ki 24:10, 2Ki 24:11), that none shall be allowed by the enemy to get out (compare Jer 13:20).