Albert Barnes Commentary Esther 9:15

"And the Jews that were in Shushan gathered themselves together on the fourteenth day also of the month Adar, and slew three hundred men in Shushan; but on the spoil they laid not their hand." — Esther 9:15 (ASV)

Shushan - Here probably the lower town, which lay east of the upper one, and was of about the same size (compare the Esther 9:6 note).