Charles Ellicott Commentary Judges 1:18

"Also Judah took Gaza with the border thereof, and Ashkelon with the border thereof, and Ekron with the border thereof." — Judges 1:18 (ASV)

Took Gaza ... Askelon ... Ekron. — Three of the five Philistine chief cities, to which the Septuagint adds Ashdod (Azotus). In Joshua 13:3, these five townships are mentioned as still unconquered, and here the Septuagint inserts a negative—“Judah did not inherit Gaza, nor,” etc. St. Augustine had the same reading.

It is, however, possible that the word “not” was conjecturally added due to the apparent discrepancy between this passage and Judges 3:8; or, alternatively, that the phrase “did not inherit” might be an explanatory gloss on the word “took.”

Josephus (Antiquities 5.2.4) states that Ashkelon and Ashdod were taken in the war, but Gaza and Ekron escaped because their location in the plains allowed them to use their chariots. Yet, in Antiquities 5.3.1, he says that the Canaanites re-conquered Ashkelon and Ekron. In any case, the conquest was very transitory. (Judges 3:3; Judges 3:13 and following).