The wealthy or the aristocracy class dominated the early Roman Republic. While the lower- class (plebeians) citizens had no say in government. Over time, plebeians elected their own representatives, call tribunes, who gained the power by the senate.
The history of Roman Senate goes since the beginning of Rome history; first, it was created a group of 100 member advisor group for the kings, later they 300 members, but when the kings were expelled from Rome the Senate became the most powerful governing body.