Komentarz do Diwrej ha-jamim II 11:5

and he built cities for fortification - Heb. לְמָצוֹר. He built small cities and surrounded them with water for strength, and this is [called] מָצוֹר as it is written in Isaiah (37:25): “I dug and drank water, and I dried up with the soles of my feet all rivers of fortification (מַָצוֹר).” And this was now necessary because Israel rebelled against him.