Albert Barnes Commentary Esther 2:3

"and let the king appoint officers in all the provinces of his kingdom, that they may gather together all the fair young virgins unto Shushan the palace, to the house of the women, unto the custody of Hegai the king`s chamberlain, keeper of the women; and let their things for purification be given them;" — Esther 2:3 (ASV)

The house of the women — that is, the “gynaeceon,” or “haram” — was always an essential part of an Eastern palace (Compare 1 Kings 7:8). In the Persian palaces it was very extensive, since the monarchs maintained, besides their legitimate wives, as many as 300 or 400 concubines .