In 856 the caliph al-Mu'tassim was unhappy about clashes between the local population and his troops so he established a new capital further north on the Tigris at Samarra. During this period the power of the caliphate began to decline and control over distant provinces was loosened. Several local dynasties grew up including the Tulunids in Egypt, the Aghlabids in Ifriqiyya and the Samanids in Khurassan (eastern Iran). Internal troubles in Samarra caused the caliph al Mu'tamid to move back to Baghdad in 889; at this time Abbasid power outside Iraq was purely nominal.

In 945 the Abbasids were replaced by the Shi'a Buwaihid amirs as rulers of Iraq and Iran. For the next two hundred years the Abbasids remained nominal caliphs with no real authority. In the mid-twelfth century the Abbasids were able to reassert some authority when the Seljuk ruler Sultan Muhamad abandoned his siege of Baghdad. During the reign of Caliph al-Nasir (1179-1225) the Abbasids were able to gain control over much of present-day Iraq. The Mongol invasions and sack of Baghdad in 1258 dealt a final blow to the political aspirations of the Abbasids. Although Abbasid architecture covers a vast area from North Africa to western India, the majority of extant buildings are in the Abbasid homeland of Iraq. Abbasid architecture was influenced by three architectural traditions - Sassanian, Central Asian (Soghdian) and later, during the twelfth and thirteenth centuries, Seljuk.

Many early Abbasid structures such as the palace of Ukhaidhir bear a striking resemblance to Sassanian architecture, as they used the same techniques (vaults made without centring) and materials (mud brick, baked brick and roughly hewn stone laid in mortar), and built to similar designs (solid buttress towers). Central Asian influence was already present in Sassanian architecture but it was reinforced by the Islamic conquest of Central Asia and the incorporation of a large number of Turkic troops into the army. Central Asian influence is seen most clearly at Samarra where the wall paintings and some of the stucco work resemble that of the Soghdian palaces at Panjikent. The Abbasid architecture of the twelfth and thirteenth centuries is essentially Seljuk architecture built with Iraqi materials.

In addition to the various influences upon it, early Abbasid architecture can be seen to have developed its own characteristics. One of the most notable features of the Abbasid cities of Baghdad and Samarra is their vast scale. This is most clearly demonstrated at Samarra with its extensive palaces and mosques stretched out for more than 40 km along the banks of the Tigris. The scale of the site led to the development of new forms: thus the gieat spiral minarets of the Great Mosque and the Abu Dulaf Mosque were never repeated elsewhere (with the possible exception of the Ibn Tulun Mosque). Other developments had far-reaching consequences; for example, the three stucco types developed at Samarra rapidly spread throughout the Islamic world (e.g. the Abbasid mosque at Balkh in Afghanistan) and continued to be used centuries later. [hide description]