In cities organized along Roman lines, the bouleutic order (ordo decurionum) was made up of nobles, separately for each city, and comprised some one hundred members. Rarely, and mainly in cities in the eastern provinces, this number fluctuated at much higher levels. To the bouleutic order belonged the city's rulers and the members of its Council, who were clearly distinguished from the city's plebs. Entry into this order was not hereditary: every well-to-do male citizen over the age of 25 or 30 would be called on to serve on the Council and would hold public office. But as the son of a councillor would inherit the latter's estate, it was very frequent for certain families to belong to this order over many generations. In major trading centres the bouleutic order was made up of numerous merchants and businessmen.

It can well be understood that the composition of the bouleutic order varied from city to city, even within one and the same province of the Roman empire, while its form depended on what the social structure of a particular city was. Economic weight, cultured behaviour and descent were three factors that played a decisive role. Notwithstanding, both their work and their privileges were shared. Councillors would frequently pay the cost of erecting public buildings in the city, or go to other expense for its good, such expenses being known in Latin as munificentia (benefactions).

Frequently a city's bouleutic order would show inner diversity. This was chiefly so from the 2nd century A.D. onwards, when many councillors started to encounter economic problems and were no longer in any position to shoulder the economic burden of taking part in the order. Clazomenae in Asia Minor affords a typical example. Here the bouleutic order had two sub-groups during the period of Hadrian's administration: the viri primores and the viri inferiores, meaning respectively the 'upper men' and the 'lower men'.