SPQR is an initialism from a Latin phrase, Senātus Populusque Rōmānus ("The Senate and the People of Rome" or "The Senate and Roman People"), referring to the government of the ancient Roman Republic, and used as an official signature of the government. It appears on coins, at the end of documents made public by inscription in stone or metal, in dedications of monuments and public works, and was emblazoned on the standards of the Roman legions. The phrase appears many hundreds of times in Roman political, legal and historical literature, including the speeches of Marcus Tullius Cicero and the history of Titus Livius. Since the meaning and the words never vary, except for the spelling and inflection of populus in literature, Latin dictionaries classify it as a formula.
This signature continued in use under the Roman Empire. The emperors were considered the representatives of the people even though the senatus consulta, or decrees of the Senate, were made at the pleasure of the emperor.
Populus Romanus in Roman literature is a phrase meaning the government of the Republic. When the Romans named governments of other countries they used populus in the singular or plural, such as populi Priscorum Latinorum, "the governments of the Old Latins". Romanus is the established adjective used to distinguish the Romans, as in civis Romanus, "Roman citizen". The locative, Romae, "at Rome", was never used for that purpose. The Roman people appear very often in law and history in such phrases as dignitas, maiestas, auctoritas, libertas populi Romani, the "dignity, majesty, authority, freedom of the Roman people." They were a populus liber, "a free people." There was an exercitus, imperium, iudicia, honores, consules, voluntas of this same populus: "the army, rule, judgments, offices, consuls and will of the Roman people". They appear in early Latin as Popolus and Poplus, so the habit of thinking of themselves as free and sovereign was quite ingrained.
The Romans believed that all authority came from the people. It could be said that similar language seen in more modern political and social revolutions directly comes from this usage. People in this sense meant the whole government. The latter, however, was essentially divided into the aristocratic Senate, whose will was executed by the consuls and praetors, and the comitia centuriata, "committees of the hundreds", whose will came to be safeguarded by the Tribunes.
In more official contexts therefore Senatus Populusque Romanus was used for signing-off purposes. The singular was used for the nominative case. The plural could be used in other cases: senatu populoque consentientibus, "the senate and people ratifying" (an ablative absolute construction). In society SPQR was often "bully" language, the same as threatening to report or prosecute someone today.
The usage has been revived in modern times, throughout Europe and beyond. SPQ- is sometimes used as an assertion of municipal pride and civic rights. Reggio Emilia has SPQR in its coat of arms, standing for "Senatus Populusque Regiensis". There have been reports of SPQ- from:
There is an international Roman revivalist organization, Nova Roma, whose use-protected trade mark is also the famous four letters.