 The period of the kingdom can be divided into two epochs based on the legends , handed down to us principally in the first book of Livy 's Ab <unk> condita ( " From the City Having Been Founded " , or simply " History of Rome " ) . While the specific legends were probably not true , they were likely based on historical fact . It is likely that , before the founding of the republic , Rome actually had been ruled by a succession of kings . The first legendary epoch saw the reigns of the first four legendary kings . During this time , the political foundations of the city were laid , the city grew increasingly organized , the religious institutions were established , and the senate and the assemblies evolved into formal institutions . The early Romans were divided into three ethnic groups . The families that belonged to one of these ethnic groups were the original Patrician families . In an attempt to add a level of organization to the city , these Patrician families were divided into units called curia . The vehicle through which the early Romans expressed their democratic impulses was known as a " committee " ( comitia or " assembly " ) . The two principle assemblies that formed were known as the Curiate Assembly and the Calculate Assembly . The two assemblies were designed to mirror the ethnic divisions of the city , and as such , the assemblies were organized by curia . The vehicle through which the early Romans expressed their aristocratic impulses was a council of town elders , which became the Roman senate . The elders of this council were known as patres ( " fathers " ) , and thus are known to history as the first Roman senators . The demos ( " people " ) and the elders eventually recognized the need for a single political leader , and thus elected such a leader , the rex ( Roman King ) . The demos elected the rex , and the elders advised the rex . 
