<P> Arabic poetry reached its greatest height in the Abbasid era, especially before the loss of central authority and the rise of the Persianate dynasties . Writers like Abu Tammam and Abu Nuwas were closely connected to the caliphal court in Baghdad during the early 9th century, while others such as al - Mutanabbi received their patronage from regional courts . </P> <P> One of the common definitions for "Islamic philosophy" is "the style of philosophy produced within the framework of Islamic culture ." Islamic philosophy, in this definition is neither necessarily concerned with religious issues, nor is exclusively produced by Muslims . Their works on Aristotle was a key step in the transmission of learning from ancient Greeks to the Islamic world and the West . They often corrected the philosopher, encouraging a lively debate in the spirit of ijtihad . They also wrote influential original philosophical works, and their thinking was incorporated into Christian philosophy during the Middle Ages, notably by Thomas Aquinas . </P> <P> Three speculative thinkers, al - Kindi, al - Farabi, and Avicenna, combined Aristotelianism and Neoplatonism with other ideas introduced through Islam, and Avicennism was later established as a result . Other influential Abbasid philosophers include al - Jahiz, and Ibn al - Haytham (Alhacen). </P> <P> As the power shifted from the Umayyads to the Abbasids, the architecture styles changed also . The Christian styles evolved into a style based more on the Sasanian Empire utilizing mud bricks and baked bricks with carved stucco . Another major development was the creation or vast enlargement of cities as they were turned into the capital of the empire . First, starting with the creation of Baghdad, starting in 762, which was planned as a walled city with a mosque and palace in the center . The walls were to have four gates to exit the city . Al - Mansur, who was responsible for the creation of Baghdad, also planned the city of Raqqa, along the Euphrates . Finally, in 836, al - Mu'tasim moved the capital to a new site that he created along the Tigris, called Samarra . This city saw 60 years of work, with race - courses and game preserves to add to the atmosphere . Due to the dry remote nature of the environment, some of the palaces built in this era were isolated havens . Al - Ukhaidir Fortress is a fine example of this type of building which has stables, living quarters, and a mosque, all surrounding inner courtyards . Other mosques of this era, such as the Mosque of Ibn Tulun, in Cairo, and the Great Mosque of Kairouan in Tunisia while ultimately built during the Umayyad dynasty, it was substantially renovated in the 9th century . This renovation was so extensive as to ostensibly be a rebuild, was in the furthest reaches of the Muslim world, in an area that the Aghlabids controlled; however the styles utilized were mainly of the Abbasids . Mesopotamia only has one surviving mausoleum from this era, in Samarra . This octagonal dome is the final resting place of al - Muntasir . Other architectural innovations and styles were few, such as the four - centered arch, and a dome erected on squinches . Unfortunately, much was lost due to the ephemeral nature of the stucco and luster tiles . </P>

Which event divides abbasid rule into its 'early' and 'late' eras