Islam, established in the 7th century, organized its army and subjugated surrounding areas in a twinkling, making the great Arabic Empire covering Egypt, Syria, Turkey, and Persia.
Since Muslims were to worship God five times a day, a mosque was needed on a spot at every conquered place. On the battlefront, they often provided a �efield mosque�f by simply drawing a line to demarcate the worship space on the ground, indicating the direction of Makka, while in a subjugated city, it was easiest to requisition an existing building.

As the Christian Roman Empire ruled the Middle East before the Muslim conquest, every town had Christian churches. Muslims used to requisition these religious facilities anywhere they conquered, sharing them with Christians at the beginning, then gradually altering them into the exclusive mosques in accordance with the Islamization of people.

 
Courtyard and Capital of Cloisters, Ulu Cami

One of the oldest mosques in Turkey, the Ulu Cami (Great Mosque) in Diyarbakir followed a course like this. The origin of this city, which was referred to as Amida in ancient times, goes back to before the Common Era, and suffered painful vicissitudes of incessant occupations by Roman, Persian, Byzantine, and Arabic Empires due to its vulnerable geographical position to neighboring enemies.
The initial period of this mosque precedes the immigration of Turks from the East, therefore it can be said that Diyarbakir was a Syrian city rather than Turkish.

There was a Christian Cathedral in this city, St. Thomas, used by Muslims and Christians in common. After having its use divided by the time or day, two thirds of the building was likely to be occupied by Muslims in around 770. It was completely converted to a mosque in accordance with the conversion of people into Islamic faith. The current mosque is the reconstructed building of the 11th century by the Turkic Seljuqids.

The Ulu Cami faces the main street penetrating the city from north to south, but the length of it is about 30m only, less than ten per cent of its total circumference of 320 meters. The other periphery gets totally buried in the urban fabric, having barely the external appearance of a building. It indicates well the character of Islamic architecture that does not intend to flaunt an imposing monumental air.

PLAN of Ulu Cami, Diyarbakir
(From "The Art and Architecture of Turkey" by Ekrem Akurgal, 1980)

One enters through a large arched opening on the stone wall facing the main street down a flight of stairs into the large oblong courtyard, on the south side of which lies the main worship hall. This hall, full length of the precinct, is an extremely oblong room with shallow depth, providing expansive Kibla wall facing the direction of Makka. The central nave has a wider span and a higher ceiling with a wing of two large and long arcades on both sides.

Actually, this mosque-form had a model in Damascus, the capital of Syria. It was the Great Mosque of the 8th century, dubbed the Umayyad Mosque because it represented the Umayyads, the first Islamic dynasty. In that site too there had been a Christian church, St. John�fs Cathedral, which Muslims dismantled in order to build a quite oblong worship hall there, using the old four rows of arcades in the two new wings on both sides of the central nave.

Other than that, one can see the resemblances throughout the two mosques; no external appearance apart from the main entrance, installation of an ablution fountain and an octagonal bower in the courtyard, a square minaret modeled after Christian bell towers, etc. It is the result of the Seljuq sultan Malikshah (1055-92) wanting to deliver the glory of Damascus to Diyarbakir in southern Turkey.

 
Mihrab and Minbar, and ceiling of Worship Room

The differences from Damascus are the absence of a dome in the center of the worship hall, thick pillars instead of round columns at the arcades, and entire lack of ornamentation of mosaics, circumstances which give this mosque the impression of more simplicity and fortitude suitable for Islamic architecture.

Nevertheless, the method that, instead of erecting a sculptural main edifice in the center of the site, one reverses wholly such a usual formation of religious facility, inserting a vacant space as a courtyard in the center of the site, putting all buildings aside to the circumference, is completely the same as the former and quite unique in the history of religious architecture in the world.

This architectural formation following the Umayyad Mosque in Damascus was executed in Aleppo and Hama in Syria and other cities, but it did not become the main stream of mosque architecture in the Islamic world. In particular, Turkey has changed the method into covering a mosque with a huge dome since the inauguration of the Ottoman dynasty, establishing a distinctly different mosque-form (i.e. the Turkish-type) from the Arabic type.

(In "Chugai Nippo" 2004)