“Ulu Cami” (The Grand Mosque) was built by Yıldırım Bayezid between 1396 and 1399. After the victory at Nicopolis (Niğbolu) in 1396, Yıldırım Bayezid wanted to built 20 masjids in Bursa, but on suggestion of Emir Sultan, his son-in-law and one of the period’s important scolar men, he built only one, the “Ulu Cami”, or Grand Mosque, covering it with 20 domes. 

This mosque became the largest example of multi-domed mosque architecture within Ottoman architecture. By the period’s scholar men, “Ulu Cami” is recognized among the holy places within Islam as to be on the fifth place (after Mecca, Medina, Jerusalem and Damascus). “Ulu Cami” is built with a rectangular plan. It has three doors, one each at its eastern, western, and northern façade. The crown door at the structure’s northern façade is more majestic compared to the other ones. This door is built of marble. 

This mosque is covered with 20 domes with a diameter of 11 m each. They sit on arches and pendatives, which interconnect the twelve massive, square-plan pillars to the thick main walls. The dome at this mosque’s central section is covered with a glazing. Beneath it, there is a big ablution fountain with 16 corners.

This mosque’s interior is decorated with 129 writings, some of which being written by famous calligraphers such as Abdulfettah Efendi, Mustafa Izzet Efendi, Sami Efendi, and Shefik Efendi. These writings are presented as authentic examples of calligraphy. There are copies of Asma-ul Husna, the 99 names of Allah, written with “celi sulus” and “kufi” script all over these pillars. Furthermore, there is a caligraphic writing by Sultan Mahmud II.

This mosque’s pulpit is made in “kundekari” technique  without using nails or any other joining elements. Therefore, it has the character of an artwork. It was built by Hadji Muhammed bin Abdulaziz bin Ibnu’d-Devaki. The reliefs at the pulpit’s eastern and western side represent the solar system and the Milky Way galaxy, respectively. Furthermore, the epitaph board over the pulpit’s door states that this mosque was completed in 1399, by the order of Yıldırım Bayezid.