The previous answer gave a good snapshot of Rome, but one must also keep in mind the following points:
1. Not much is know about Rome from a historical perspective during the early stages. One can even argue that not much is known before the 3rd century BC.
2. Rome lasts a very long time. Therefore, the previous answer only reflects a certain period of republican Rome. For instance, Sulla, a dictator, increases the senate from 300 to 600.
3. After Julius Caesar, there are emperors. This radically changes the government in many ways. For example, if the emperor gave a decree, this decree now became de facto a law.
4. There are also a number of jurists who help the praetor with aspects of the law. Praetors were not experts in law. So, they needed this technical information and the jurists were the ones who gave it.
5. Jurists also wrote about matters of law. We have many of their writings through various later books. Justinians' Digest is the largest body of law that we currently possess.
Rome began as a monarchy, however in 509 B.C.E. The Roman Republic was born. The political structure of the Republic (at its fully developed stage) was not a democracy however,the 'res-republic' when translated meant 'property of the people'. The political and judicial structure within the republic was separated between The Magistrates (officials) and The Senate and The People (SPQR) Senatus-Popalusque-Romanus... 'The Senate and People of Rome'. The specific titles are included below:
1. Consuls- commander and chief, 1 year term, two
2.Dictator- appointed only in times of crisis
3.Censors- in charge of the census, supervised public morals
4.Praetor-in charge of the courts
5.Quaestor-the 'go-for' in charge of treasury and public records
6.Tribunes-protect the common people (pleblieans) from abuse of patrician power
7.Aediles-maintained public roads,bridges,buildings,and games
The Senate-100 men of patrician class, voting power- job was for life, duties included passing laws,setting requirements regarding judicial matters, advisement, budget, and taxes.
The Cursus Honorum-the well born Roman who climbs the ladder of success
The Priests-represent the state religion, 'The Rex Sacrorum- 'King of Sacred Rites', 'The Pontifics'-college of priets, 'The Pontifex Maximus'-chief priest that oversaw the Vestal Virgins