The judex and the arbiter had the same functions, and apparently the only express basis for the distinction between the two words is that there might be several arbitri but never more than one judex in a cause.
In the civil law the judex ordinarius is a judge who has regular jurisdiction as of course and of common right as opposed to persons extraordinarily appointed.
The phrase judex arbiterve frequently occurs.
The praetor, who had the arrangement of all trials or private suits and the formal appointment of judges for them, referred the great majority of such cases for decision to a judge who was styled usually judex but sometimes arbiter.
Describes him as judex ordinarius, and he possesses in his own right the powers of visitation, of holding courts and imposing penalties, of deciding in matrimonial causes and cases of disputed jurisdiction, of testing candidates for orders, of inducting into benefices.
Little is known of the condition of the subject populations of the peninsula during the Arab occupation; but we are informed that the Christians were, sometimes at least, judged according to their own laws in separate tribunals presided over by Christian judges; 2 and the mere fact of the preservation of the name alcalde, an official whose functions corresponded so closely to those of the judex or defensor civitatis, is fitted to suggest that the old municipal fora, if much impaired, were not even then in all cases wholly destroyed.