The praetorship was originally a kind of third consulship. The Latin word "praetor" means literally "who goes before", "who precedes" and we can translate it as "president", "leader" and "commander".
Originally there was one praetor elected as minor colleague to the consules. The praetor could command the armies of the state; and while the consuls were absent with the armies, he exercised their functions within the city. He was a magistratus curulis and he had the imperium, and consequently was one of the magistratus maiores: but he owed respect and obedience to the consuls (Polyb. XXXIII.1). He had the right to sit in the sella curulis, to wear the toga praetexta and was attended by six lictors, whence he is called by Polybius ἡγεμὼν or στρατηγὸς ἑξαπέλεκυς, and sometimes simply ἑξαπέλεκυς. Plutarch (Sulla, 5) uses the expression στρατηγία πολιτική. At a later period the praetor had only two lictors in Rome (Censorinus, c24).
The praetorship was at first given to a consul of the preceding year as appears from Livy. L. Papirius was praetor after being consul (Liv. X.47) but later it became a rule to assume the praetura before running for the consulatus.
In the year B.C. 246 another praetor was appointed, whose business was to administer justice in matters in dispute between peregrini, or peregrini and Roman citizens; and accordingly he was called praetor peregrinus (Dig. 1 tit. 2 s23). The other praetor was then called praetor urbanus "qui jus inter cives dicit" and sometimes praetor Urbis.
Extracted from Lacus Curtius