Both Turks and Arabs were nomadic in origin, and there are still numbers of nomads in Turkey. Persian civilisation in the Arab 'Iraq is likewise completely ruined. Formerly, the whole region between the Sudan and the Mediterranean had been settled. This assessment is, of course, valid only for his own time. Ibn Khaldun was fascinated by architecture, and especially by the constructions of the ancients.
Parties assemble for the purpose.
He may well have made many of these during his time in Turkey so that, in the absence of parallel accounts, we may use it as a model for what happened in Turkey - a model easily confirmed by observation. The civilization of the city then recedes, and its inhabitants decrease in number. This entails a decrease in the crafts. The materials that are in existing buildings are re-used for building and refinishing. People then return to the Bedouin way of building.