The Abbasids and their Vassals
The architecture of the Abbasids presents what may be referred to as the first 'Classical' moment in the evolution of Islamic architecture, one that was centred in the political and cultural capital of the Abbasid state, Baghdad (and by extension the adjacent royal suburb of Samarra). The Abbasid architecture of Baghdad was dominated by the use of brick as a construction material. Stucco is also widely used as a sheathing material. Stone was used in areas of the Abbasid state where it was a predominant or at least common building material, as in Tulunid Egypt and Aghlabid Tunisia, the two main Abbasid-era traditions represented in this project. Wood is also used, though more sparingly, for elements such as the minbar, doors and in the building's beams.

The hypostyle-mosque plan continues to be the primary mosque plan. The minaret, minbar and mihrab become standard features in mosques. The relatively small dome located over the area in front of the mihrab, which first emerged during the Umayyad period, becomes a widespread element. In the case of Aghlabid architecture, a second dome is also sometimes constructed, opposite the first dome, at the entrance leading from the courtyard to the prayer hall. Another development dating to the Abbasid period is the appearance of the ziyada, the open space that surrounds the mosque and separates it from the surrounding urban fabric.

The uniquely Islamic architectural element of the muqarnas makes its first appearance during the Abbasid period, probably in Baghdad. The first examples have been dated to the late AH 3rd / AD late 9th–early 10th centuries, and it spread throughout the central Islamic lands during the 5th / 11th century. The pointed arch becomes a predominant feature during the Abbasid period, and the horseshoe arch emerges as a common element in the architecture of the Aghlabids. In terms of building types, the appearance of funerary architecture in Islamic architectural traditions dates to the Abbasid period. Initially these consisted of a single space covered by a dome.

The primary decorative motifs of the period were stylised vegetal motifs as well as geometric patterns which were often executed in stucco. The 'arabesque' or repeated, interlaced stylised vegetal motif also comes into being during this period. Inscriptions continue to play an integral role in the articulation of architecture.

The earlier examples of Abbasid architecture show clear Sassanian influences from Iran. However, the architecture of Aghlabid Tunisia shows a higher level of continuity with Umayyad traditions. Examples of this include the use of minarets with square sections, and the re-use of Roman and Byzantine building components, such as column shafts and capitals. By the early 3rd / mid-10th century, especially with the emergence of what is referred to as the 'Samarra style', the architecture of the Abbasids could be described as self-referential, evolving through an internal process that relied primarily on Muslim prototypes rather than styles imported from other traditions.
Hegira 247 / AD 861
Cairo, Egypt
The Nilometer is an example of Tulunid architecture for which stone is a primary construction material.