The Philistine cities of Ashdod and Ashkelon were located on or near the coast, while Ekron was inland. Gath is not mentioned here because Hazael had conquered it earlier (2 Kings 12:17), followed by Uzziah (2 Chronicles 26:6).
the remnant of the Philistines: They kept their ethnic identity during the Assyrian period, but this distinction disappeared by the time of the Persians (Zechariah 9:5–7).