The Valerian and Porcian laws were Roman laws passed between 509 BC and 184 BC. They exempted Roman citizens from degrading and shameful forms of punishment, such as whipping, scourging, or crucifixion. They also established certain rights for Roman citizens, including Provocatio, the right to appeal to the tribunes of the plebs. The Valerian law also made it legal to kill any citizen who was plotting to establish a tyranny. This clause was used several times, the most important of which was its usage by Julius Caesar's assassins.
The first Valerian law was enacted by Publius Valerius Publicola in 509 BC, a few years after the founding of republican Rome. It allowed a Roman citizen, condemned by a magistrate to death or scourging, the right of appeal to the people (Provocatio ad Populum), that is, to the people composed of senators, patricians, and plebeians. Thus the consuls no longer had the power of pronouncing sentence in capital cases against a Roman citizen, without the consent of the people. The Valerian law consequently divested the consuls of the power to punish crimes, thereby abolishing the vestiges within the Roman government of that unmitigated power that was the prerogative of the Tarquin kings.
Nonetheless, the Valerian law was not kept on the books throughout the five hundred years of the Roman republic. Indeed, Titus Livius (Livy) states that the Valerian law was enacted again, for the third time, in 299 BC. Andrew Lintott surmises that the effect of this third Valerian law was to regularize the provocatio: appeals from the people via the Tribune of the Plebs had been a fact of life with which magistrates had to deal prior to the law, but now magistrates were ordered to yield to the decisions of the people in capital cases. Livy notes that in all three cases the law was enacted by the Valerius family. Furthermore, Livy notes that, should a magistrate disregard the Valerian law, his only reproof was that his act be deemed unlawful and wicked. This implies that the Valerian law was not so very effective in defending the plebs.
The Porcian Laws (Latin: Leges Porciae) were three Roman laws broadening the rights of the Valerian law. They were enacted by members of the Gens Porcia in the 2nd century BC. We do not know their precise dates, but they seem to have ended summary execution of Roman citizens in the field and provinces and provided that citizens could escape sentences of death by voluntary exile. Cicero in the Republic (2.54) refers to three leges Porciae, but is not clear on their specific details.
Another law that was passed with the intention of protecting citizens from severe punishment at the hands of governors and magistrates, is the lex Julia de vi publica, passed around 50 BC. Yet this law, for all practical purposes, is only a restatement of the right of appeal present in the Valerian and Porcian laws.
This sanctity of a citizen's person was highly esteemed by the Romans, and so any violation of the Valerian and Porcian laws was deemed to be almost a sacrilege. Cicero’s oration in his prosecution of Verres indicates the high pitch to which this feeling was carried. Verres, who as the governor of Sicily (73 - 70 BC) had a number of Roman citizens cruelly killed, was eventually tried before the senators in Rome, on charges of extortion (Cic. Ver. 5.161-2).