'Castle' in the Bible

It happened, when Zimri saw that the city was taken, that he went into the castle of the king's house, and burnt the king's house over him with fire, and died,

Pekah the son of Remaliah, his captain, conspired against him, and struck him in Samaria, in the castle of the king's house, with Argob and Arieh; and with him were fifty men of the Gileadites: and he killed him, and reigned in his place.

that I put my brother Hanani, and Hananiah the governor of the castle, in charge of Jerusalem; for he was a faithful man, and feared God above many.

A brother offended is more difficult than a fortified city; and disputes are like the bars of a castle.