What responsibilities did a judex have in a classical Roman civil case?

In a classical Roman civil case, the judex was not a magistrate or a lawyer, but a prominent layman selected by the parties to the dispute to preside over the second stage of the trial.1

His primary responsibilities included:

• Hearing the Case: Unlike the formal, rigid preliminary hearing held before a magistrate, proceedings before the judex were informal. He oversaw the presentation of evidence, heard from advocates, and listened to witnesses.12
• Rendering a Decision: Under the formulary system, the judex followed written instructions provided by the magistrate. These instructions typically took the form of a conditional order: if the facts presented proved the plaintiff's claim, the judex was to condemn the defendant to pay; if not, he was to absolve the defendant.2
• Limitations: The judex lacked the authority to enforce his own decisions. If a defendant failed to comply with the judgment, the plaintiff was responsible for bringing the matter back to the magistrate to seek enforcement, which could result in the seizure of property or, in earlier periods, the enslavement of the defendant to satisfy the debt.12