The family was the basic unit in ancient Rome. The father, who headed the family, is said to have held the power of life and death over his dependents. This arrangement was repeated in the overarching political structures, but was moderated by the voice of the people.
It Started With a King at the Top
"As the clans resting upon a family basis were the constituent elements of the state, so the form of the body-politic was modelled after the family both generally and in detail."
The 7th and final king, Tarquinius Superbus, was an Etruscan who was removed from office by some of the leading men of the state. Lucius Junius Brutus, an ancestor of the Brutus who helped assassinate Julius Caesar and usher in the age of emperors, led the revolt against the kings.
With the king gone (he and his family fled to Etruria), the top power holders became the two annually-elected consuls, and then later, the emperor who, to some extent, reinstated the role of the king.
The basic unit of Roman life was the familia 'family', consisting of the father, mother, children, slaves, and clients, under a paterfamilias 'father of the family' who was responsible for making sure the family worshiped its household gods (Lares, Penates, and Vesta) and ancestors.
The power of the early paterfamilias was in theory absolute: he could even execute or sell his dependents into slavery.
Gens:Descendants in the male line either by blood or adoption are members of the same gens. The plural of a gens is gentes. There were several families in each gens.
Patron and Clients:
Clients, who included in their number manumitted slaves, were under the protection of the patron. Although most clients were free, they were under the paterfamilias-like power of the patron. A modern parallel of the Roman patron is the sponsor who helps with newly arrived immigrants.
The early plebeians were the common people. Some plebeians had once been slaves-turned-clients who then became completely free, under state protection. As Rome gained territory in Italy and granted citizenship rights, the number of Roman plebeians increased.
The king was the head of the people, chief priest, leader in war, and the judge whose sentence couldn't be appealed. He convened the Senate. He was accompanied by 12 lictors who carried a bundle of rods with a symbolic death-wielding axe in the center of the bundle (the fasces). However much power the king had, he could be kicked out. After the expulsion of the last of the Tarquin kings, the 7 kings of Rome were remembered with such hatred that there were never again kings in Rome.
The council of fathers (who were heads of the early great patrician houses) made up the Senate. They had lifetime tenure and served as an advisory council for the kings. Romulus is thought to have named 100 men senators. By the time of Tarquin the Elder, there may have been 200. He is thought to have added another hundred, making the number 300 until the time of Sulla.
When there was a period between kings, an interregnum, the Senators took temporary power. When a new king was picked, given imperium by the Assembly, the new king was sanctioned by the Senate.
The earliest assembly of free Roman men was called the Comitia Curiata. It was held in the comitium area of the forum. The curiae (the plural of curia) were based on the 3 tribes, Ramnes, Tities and Luceres. Curiae contained several gens with a common set of festivals and rites, as well as shared ancestry.
Each curia had one vote based on the majority of the votes of its members. The assembly met when called by the king. It could accept or reject a new king. It had power to deal with foreign states and could grant change in citizenship status. It witnessed religious acts, as well.
Following the end of the regal period, the Assembly of the people could hear appeals in capital cases. They annually elected rulers and had the power of war and peace. This was a different Assembly from the earlier tribal one and was the result of a re-division of the people. It was called the Comitia Centuriata because it was based on the centuries used to supply soldiers to the legions. This new Assembly did not entirely replace the old one, but the comitia curiata had much reduced functions. It was responsible for confirmation of the magistrates.
This is the redistribution of the people that led to the change in the comitia.
For the Romans, power (imperium) was almost a tangible. Having it made you superior to others. It was also a relative thing that could be given to someone or removed. There were even symbols -- the lictors and their fasces -- the powerful man used so those around him could immediately see that he was filled with power.
Imperium was originally the lifelong power of the king. After the kings, it became the power of the consuls. There were 2 consuls who shared imperium for a year and then stepped down. Their power was not absolute, but they were like dual annually-elected kings.
During war, consuls had the power of life and death and their lictors carried axes in their fasces bundles. Sometimes a dictator was appointed for 6 months, holding absolute power.
In peace the authority of the consuls could be challenged by the assembly. Their lictors left the axes out of the fasces within the city.
Some of the ancient writers about the period of the Roman kings are Livy, Plutarch, and Dionysius of Halicarnasus, all of whom lived centuries after the events. When the Gauls sacked Rome in 390 B.C. -- more than a century after Brutus deposed Tarquinius Superbus -- the historical records were at least partially destroyed. T.J. Cornell discusses the extent of this destruction, both in his own The Beginnings of Rome: Italy and Rome from the Bronze Age to the Punic Wars (c.1000-264 BC) and in The Cambridge Ancient History Volume 7, Part 2: The Rise of Rome to 220 BC by F. W. Walbank and A. E. Astin. As a result of the destruction, however devastating or not, the information about the earlier period is unreliable.