Though the periods in which these systems were in use overlapped one another and did not have definitive breaks, the legis actio system prevailed from the time of the XII Tables (c. 450 BC) until about the end of the 2nd century BC, the formulary procedure was primarily used from the last century of the Republic until the end of the classical period (c. AD 200), and cognitio extra ordinem was in use in post-classical times.
The remarkable aspect of a trial of an action under the legis actio procedure (and also later under the formulary system) was characterized by the division of the proceedings into two stages, the first of which took place before a magistrate, under whose supervision all the preliminaries were arranged, the second, in which the issue was actually decided, was held before a judge.
The magistrate in question taking part in the preliminary stage was typically the consul or military tribune, almost exclusively the praetor upon the creation of this office.
If the defendant could not be brought to court, he would be regarded as indefensus, and the plaintiff could, with the authorization of the praetor, seize his property.
At the first stage of the case, a hearing took place before the praetor, in order to agree the issue and appoint a judge.
Judges were chosen from a list called the album iudicum, consisting of senators, and in the later Republic, men of equestrian rank.
This was fairly informal compared to the preliminary hearing, and was supposed under the Twelve Tables to take place in public (the Forum Romanum was frequently used).
The formula was a written document by which a civil trial authorization was given to a judge to either condemn the defendant if certain factual or legal circumstances appeared to be proved, or to absolve him if this was not the case.
This part appointed a judge, in a similar matter to before, with the plaintiff suggesting names from the official list until the defendant agreed.
Thirty days after the judgement, the creditor would apply for an actio iudicati, giving the debtor a last chance to pay.
In the cognitio, however, the State basically resolved the entire case, in the same manner as virually all modern systems.
Instead, he would lodge a libellus conventionis (a statement of claim), which would be served on the defendant by a court official, who could arrest him if he failed to appear.
This highlights the philosophical difference between the cognitio and earlier systems—whereas before a trial required the consent of both parties, it could now be imposed by the state.
The process tended to be less adversarial than before, as the magistrate had sole control over the case, and could admit whatever evidence he pleased.
Documentary evidence was now considered to be of vital importance (indeed, a rule was introduced to the effect that a document could not be defeated by oral testimony alone).
Whereas before the victor was responsible for enforcing payment himself, he could now ask the court bailiffs to seize the defendant's property to be sold at auction.