After holding either the office of quaestor or aedile, a man of 39 years could run for praetor. The number of Praetors elected varied through history, generally increasing with time. During the republic, six or eight were generally elected each year to serve judicial functions throughout Rome and other governmental responsibilities. In the absence of the Consuls, a Praetor would be given command of the garrison in Rome or in Italy. Also, a Praetor could exercise the functions of the Consuls throughout Rome, but their main function was that of a judge. They would preside over trials involving criminal acts as well as grant court orders or validate "illegal" acts as acts of administering justice. As a Praetor, a magistrate was escorted by six lictors, and wielded imperium. After a term as Praetor, the magistrate would serve as a provincial governor in the office of Propraetor, wielding Propraetor imperium, commanding the province’s legions, and possessing ultimate authority within his province(s).
Of all the Praetors, two were more prestigious than the others. The first was the Praetor Peregrinus, who was the chief judge in trials involving one or more foreigners. The other was the Praetor Urbanus, the chief judicial office in Rome. He had the power to overturn any verdict by any other courts, and served as judge in cases involving criminal charges against provincial governors. The Praetor Urbanus was not allowed to leave the city for more than ten days. If one of these two Praetors was absent from Rome, the other would perform the duties of both.
Read more about this topic: Cursus Honorum