SPQR - Senātus Populusque Rōmānus

SPQR is an initialism from a Latin phrase, Senātus Populusque Rōmānus ("The Senate and People of Rome", see translation), referring to the government of the ancient Roman Republic, and used as an official emblem of the modern day comune (municipality) of Rome. 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 Mārcus Tullius Cīcerō (Tully) and the Ab urbe condita libri ("Books from the Founding of the City") of Titus Livius (Livy). Since the meaning and the words never vary, except for the spelling and inflection of populus in literature,^{[citation needed]} Latin dictionaries classify it as a formula.

Translation

In Latin, Senātus is a nominative singular noun meaning "Senate". Populusque is compounded from the nominative noun Populus, "the People", and -que, an enclitic particle meaning "and" which connects the two nominative nouns. The last word, Rōmānus ("Roman") is an adjective modifying Populus: the "Roman People".
Thus, the sentence is translated as the more literal "The Senate and the Roman People", or alternatively as "The Senate and the People of Rome".

Historical context

The title's date of establishment is unknown, but it first appears in inscriptions of the Late Republic, from c. 80 BC onwards. Previously, the official name of the Roman state, as evidenced on coins, was simply ROMA. The abbreviation last appears on coins of Constantine I the Great (ruled AD 312-37).
The two legal entities mentioned, Senātus and the Populus Rōmānus, are sovereign when combined. However, where populus is sovereign alone, Senātus is not. Under the Roman Monarchy neither entity was sovereign. The phrase, therefore, can be dated to no earlier than the foundation of the Republic.

An aureus with Augustus on the obverse and a winged victory on the reverse with SPQR above.

This signature continued in use under the Roman Empire. The emperors were considered the representatives of the people even though the senātūs consulta, or decrees of the Senate, were made at the pleasure of the emperor.
Populus Rōmānus in Roman literature is a phrase meaning the government of the People. When the Romans named governments of other countries they used populus in the singular or plural, such as populī Prīscōrum Latīnōrum, "the governments of the Old Latins". Rōmānus is the established adjective used to distinguish the Romans, as in cīvis Rōmānus, "Roman citizen". The locative, Rōmae, "at Rome", was never used for that purpose.
The Roman people appear very often in law and history in such phrases as dignitās, maiestās, auctoritās, lībertās populī Rōmānī, the "dignity, majesty, authority, freedom of the Roman people". They were a populus līber, "a free people". There was an exercitus, imperium, iudicia, honorēs, consulēs, voluntās 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 centuriāta, "committee of the centuries", whose will came to be safeguarded by the Tribunes.