Attacking them vigorously: We have expressed this clause as “a series of strong attacks” in the model for the previous verse.

They gained possession of the places: This clause may be better placed after the next one (so Good News Bible).

And beat off all who fought upon the wall: The Idumean soldiers were on the walls of the fortified cities, attempting to keep the Jewish attackers away. Judas’ men succeeded in driving the enemy soldiers off the walls, thus taking control of the cities.

And slew those whom they encountered, killing no fewer than twenty thousand: Judas’ men killed everyone they engaged in battle, at least 20,000.

Good News Bible provides a helpful model for this verse.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Maccabees. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here.