Albert Barnes Commentary 2 Kings 25:1

"And it came to pass in the ninth year of his reign, in the tenth month, in the tenth day of the month, that Nebuchadnezzar king of Babylon came, he and all his army, against Jerusalem, and encamped against it; and they built forts against it round about." — 2 Kings 25:1 (ASV)

In the ninth year ... - As the final catastrophe approaches, the historian becomes more precise and exact in his dates, marking not only the year but also the month and day on which the siege began, as well as when it closed (2 Kings 25:3). From Ezekiel 24:1, we find that on the very day Nebuchadnezzar's army appeared before Jerusalem, the event was revealed to Ezekiel in Babylonia, and the city's fate was announced to him (Ezekiel 24:6–14).

The army seems to have initially spread itself over all Judea. It fought not only against Jerusalem but especially against Lachish and Azekah (Jeremiah 34:7), two southern cities (2 Chronicles 11:9) that had probably been strongly garrisoned to maintain communication with Egypt. This division of the Babylonian forces encouraged Hophra to put his troops in motion and advance to the relief of his Jewish allies (Jeremiah 37:5).

Upon hearing this, Nebuchadnezzar withdrew from Jerusalem and likely marched to Azekah and Lachish. The Egyptians, however, retreated and returned to their own country, taking no further part in the war (Jeremiah 37:7; Ezekiel 17:17). Nebuchadnezzar then led his army back and once more invested the city. (It is uncertain whether the date at the beginning of this verse refers to the first or to the second investment.)

Forts - These were probably movable towers, sometimes equipped with battering rams, which the besiegers advanced against the walls. This brought their fighting men to the same level as their antagonists. Such towers are depicted in Assyrian sculptures.