Islamic architecture includes mosques, palaces, and fortresses. Mosques feature courtyards and minarets and are topped with domes. Fortresses protected military personnel and gave them shelter from enemies, such as the Masmak fort constructed during Mohammed bin Abdullah's reign. Palaces served as grand residences for royalty, like Topkapi Palace in Istanbul, which was home to Ottoman Sultans for 400 years. Islamic architecture had a wide influence both religiously and secularly from the founding of Islam to modern times.