<human>:  When was the senate first formed?
<bot>: The senate was first formed in the Roman Republic in 509 BC. It was a body of elected representatives who advised the Roman Senate. The senate was made up of two classes of people: the patricians and the plebeians. The patricians were the wealthy landowners, and the plebeians were the common people. The senate was the most important political body in the Roman Republic, and it was the only body that could pass laws.