'Citadel' in the Bible

These are the words of Nehemiah son of Hacaliah: It so happened that in the month of Kislev, in the twentieth year, I was in Susa the citadel.

Also, a letter to Asaph, keeper of the king's land reserve, that he should give me timber for laying the beams for the gates of the citadel of the house and for the walls of the city, and for the house which I will enter." And the king gave [permission] to me, according to the good hand of God on me.

And I gave my brother Hanani, and Hananiah the ruler of the citadel, charge over Jerusalem; for he was a faithful man and feared God above many.