The Twelve Tables of Roman society were said by the Romans to have come about as a result of the long social struggle between patricians and plebeians. After the expulsion of the last king of Rome, Tarquinius Superbus, the Republic was governed by a hierarchy of magistrates. Initially, only patricians were eligible to become magistrates and this, among other plebeian complaints, was a source of discontent for plebeians. In the context of this unequal status, plebeians would take action to secure concessions for themselves using the threat of secession. They would threaten to leave the city with the consequence that it would grind to a halt, as the plebeians were Rome's labor force. Tradition held that one of the most important concessions won in this class struggle was the establishment of the "Twelve Tables", establishing basic procedural rights for all Roman citizens in relation to each other. The drafting of the Twelve Tables may have been fomented by a desire for self-regulation by the patricians, or for other reasons.