As for Nizwa Castle, it was built by Imam Salt bin Malik Al Kharusi in the first half of the third century AH / late ninth century AD, and it was built next to the old mosque. Students of knowledge are called Sohar rooms, a headquarters for guests who come from far away to visit the imam, the military room, the imam’s library, coffee making and preparation rooms, prayer rooms in which the imam used to meet with people, a room (al-Najwa) for secret conversation, the imam’s private rooms in which he used to stay for worship, receiving guests, and dates stores. The castle is surrounded by a high defensive wall with gunspots and a small lane for soldiers.