Qaboos Tower Qaboos Tower, the oldest monument of Islamic era architecture, is 70 meters high and the tallest brick tower in the world. According to its inscriptions, Amir Shams-al-Maali ordered the construction in 1006 AD and lasted 5 years. A kind of gray mortar combined with sand is used to fortify the structure against erosion and would-be vandals. It is registered as world heritage site by UNESCO. http://whc.unesco.org/en/list/1398