The original mosque, laid out by al-Mu'tasim, soon became too small for the city's residents; it was eventually demolished by al-Mutawakkil, who replaced it by building the Great Mosque of Samarra in the vicinity of al-Hayr. This mosque, the largest in the world at the time, measured  and had 17 aisles in the prayer hall. An enclosure wall measuring  featured covered porticoes to accommodate additional worshippers. The spiral minaret,  high, still stands in the rear of the mosque.