C. F. Keil and Franz Delitzsch on 2 Kings 25:2

2Ki 25:2 “And the city was besieged till the eleventh year of king Zedekiah,” in which the northern wall of the city was broken through on the ninth day of the fourth month (2Ki 25:3). That Jerusalem could sustain a siege of this duration, namely eighteen months, shows what the strength of the fortifications must have been. Moreover the siege was interrupted for a short time, when the approach of the Egyptian king Hophra compelled the Chaldaeans to march to meet him and drive him back, which they appear to have succeeded in doing without a battle (cf. Jer 37:5., Eze 17:7).