The Roman Republic was the first stage of the development of the Roman Empire and began in 509 BCE/BC following the expulsion of the last king of Etruria named Tarquinius Superbus. The Roman Republic would last until 27 BCE/BC. This is the first definitive Roman political entity and is the earliest archaeological evidence that we have of the earliest Romans. Most of the information from this period comes from the major Roman Historians.
Following the establishment of the Roman Republic there was two elected consuls that served as the early leaders. At this time the settlement of Rome was a very small city and featured Temples and sanctuaries along with the Forum which was featured in every Roman settlement. The early Romans planned their cities and even had houses.
See Roman Oligarchy
Over time the Roman Oligarchy would develop with became the dominant power in Rome and rapidly acquired territory. This led to the growth and urbanization of Rome during which time the Greek culture was more or less absorbed into Roman culture. At this point we begin to see the trends that would lead to the development of the Roman Empire.