Why was the senate in roman so powerful?

The senate during the early republican phase was powerful because it was completely ruled by the patrician class which was a group of the most influential, wealthy and descendants of nobility.

During the later stage of the republic the senate was the seat of power because it held th emajority of power as well as land through the use of latifundia. As well as this it organised the armys which held the power in Rome.

During the empire stage the senate had very little actual power. This is because the emperors had slowly taken away those rights and taken the powers for themselves.