A the beginning of the 9th century Byzantine domination Arab presence in Mediterranean area threatened it.
When Byzantine Empire did not have anymore the military strength to occupy the region, actually abandoned Sicily. What allowed some Muslim people to plan an expedition (the group was made of Arabs, Berbers from Tunisia, Spanish Muslims and Sudanese people) that in 827 attacked Sicily to conquer it. It seems that Christian Sicily put up fierce resistance. Syracuse managed to lift the siege and other cities bolted the doors against the invader, but it was not enough. Meanwhile, Christian West started helping Arabs in order to damage Byzantine Empire(it seems that in 843 Neapolitan people helped Muslim to conquer Messina).
So Sicilian resistance began to become weaker and weaker and towards the end of the century the whole island had been taken. Palermo was the first important city that fell already in 831. At the half of 10th century Sicily and Palermo were Arab for good. During Arab domination in Palermo taxes became significantly lower than under Byzantine Empire. Moreover, Arab improved agricultural technology, for instance they introduced in Europe a new irrigation system. In addition, it seems that they started rice cultivation and brought a new type of wheat.
Culture flourished in the city and Emirs promoted literature and philosophy. As well remarkable was the huge hydraulic engineering work built by Arabs in Palermo: the so-called ‘Qanat’, that is a net of very long underground tunnels used to convey water throughout the city. Nowadays you can still visit them.
Arab Palermo reached a considerable number of inhabitants (more than 100.000). Unfortunately, the great number of buildings erected by Arabs was mostly destroyed by Normans and by time (in fact, the most used construction material was tuff, that is not very resistant). All we have are the works made by Islamic artists that remained in Palermo after Norman occupation.
Arab domination started tottering around the begin of year 1000. The continuous internal contradictions of the Islamic world caused actual civil wars in Sicily. During the first half of the 11th century Byzantine troops led by Maniakes tried to reconquer the island. When Byzantium recalled Maniakes the conquest stopped and Norman troops led by Count Roger attacked and ended Arab Sicily and Palermo.