After the people of ancient Rome expelled the despotic Tarquinius Superbus in 509 BC, they vowed never again to serve another king. Reassembling the remnants of their kingdom into a republic, Tarquinius’ traumatized subjects adopted a constitution whose checks and balances would prevent power from concentrating in the hands of any individual.

Instead of one king, the Roman Republic was ruled by two consuls. These consuls were nominated by the Senate and chosen by the Comitia Centuriata, a popular assembly. Each consul could veto the other’s decisions. Both were dependent on the Senate to implement their executive orders.