A paragraph break is appropriate here (so Revised Standard Version).

Then the foreigners who were in the strongholds that Bacchides had built fled: See 1Macc 9.50-52. This happened while the walls of Jerusalem were being repaired. So the connector Then may be expressed as “At that time.” The foreigners who were in the strongholds that Bacchides had built refers to the Syrian soldiers who were stationed in these forts. (Bacchides had not built the fort in Jerusalem, which continued to be occupied.) Fled may be rendered “fled back to their own land.”

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.