The Ulugbek Madrasah was built between 1417 and 1420. Its huge entrance portal is decorated with a 15 m. arch. A mosaic panel above the arch depicts a symbolic sky with five and ten- pointed stars. The Madrasah’s size is 56x81m. Inside there is an open yard (30×40 m) with an octagonal hauz in the center. The madrasah had a platform for astronomical observations made before Ulugbek’s observatory. The madrasah had fifty cells for one hundred students. Sheikh Khadja Ahrar and the poet Abdurrahman Djami were among the outstanding graduates of the madrasah. In the 18th century the second floor and the domes on the sides were dismantled. By the 20th century most of mosaic decoration on the facades had been lost, so the outstanding monument needed extensive restoration work. In the 20th century the northeastern and southeastern minarets were repaired, new domes installed, the portal arch and tympan restored.