The Hisar Mosque, one of Izmir’s landmarks, is situated at 899th Street to the east of the Kızlarağası Hanı, in the Kemeraltı-Hisarönü region. Surrounded by a narrow courtyard, the mosque consists of a harim with a central plan, a last congregation section with seven domes to the north, and a minaret at the north-west. It accommodates three fountains, a library, and a muvakkithane (time keepers office for designating the prayer times) in the courtyard, and two shadirvans outside the courtyard. The mosque was named Hisar (Fortress) after the Lower/Port Fortress that used to provide protection for the city. The Lower/Port Fortress no longer exists.
It is considered as the oldest mosque in the Kemeraltı district, but information is inconsistent regarding its construction date. Evliya Çelebi, who had visited the city in 1671-72, mentions that the building, which he refers to as the Molla Yakub Bey Mosque, was built by Yakub Bey in 1591-92. He also mentions that it has three gates, three mihrabs, and a roof which was covered partly with tiles and partly by lead-coating, and that there was an ablution pool between the mosque and the fort’s gate. In some sources, the construction date is cited as 1597. There is no information about the identity of Yakub Bey, who is considered the mosque’s patron.