The citizens of Constantinople and other large cities such as Antioch, Alexandria, Ephesus, Miletos, Priene, Jerusalem and Nea Anchialos, were organized into demoi (factions). It is not known whether the whole or only a part of the population (and how many) were so organized. Demoi were not civic bodies, although the demarch , the person in charge of the demoi of Constantinople, was appointed by the emperor. He was in charge of managers who decided and acted according to the broader political, social and religious inclinations of the demos they represented. Initially demoi were sports unions responsible for organizing horse races and other events at the hippodrome. Yet, over the course of time, they acquired political powers thanks to their organization, the fanaticism of their followers and the popularity they enjoyed with broader sections of the population. Precisely because they were the only organized popular groups, demoi undertook other responsibilities, either through their own initiative or by official demand. Such responsibilites included helping with the organization of the city defense in times of emergency.

In Constantinople, Antioch and Alexandria, the demoi of the Greens (Paasinoi) and the Blues (Venetoi), again, initially sporting groups, grew into influential political entities in Early Byzantine times, especially from the reign of Theodosios II (408-450) to the accession of Herakleios (610). The Reds (Rousioi) sided with the Greens and the Whites (Leukoi) with the Blues in Constantinople. The demoi we know were named after the colours of the emblems that sport unions employed in the Roman Empire.