The fundamental principle of the Islamic society is the "ummah", or "" (), the community of Muslims of whom each individual is equally submitted to Allah under the common law of sharia, which also subjected the respective ruler, at least nominally. In Abbasid times, some cities like the Round city of Baghdad were constructed from scratch, set up to a plan which focused on the caliph's residence, located in the very centre of the city, with main roads leading radially from the city gates to the central palace, dividing individual tribal sections with no interconnection, and separated from each other by radial walls. However, these efforts were of short duration only, and the original plan soon disappeared and gave way to succeeding buildings and architectural structures.