Written between written December of 69 and January of 70 CE, the Lex de imperio Vespasiani, or lex Regia, ratified by the Roman senate, is the only example of an official document conferring powers to an emperor. The law confirms Vespasian’s total control over the political, administrative, and religious life of the empire. This document, preserved in the Hall of the Faun in the Palazzo Nuovo of the Capitoline Museum in Rome, was cast in bronze, 164 x 113 cm. Its first sentence is incomplete, indicating that at least one other bronze plaque, presumably of the same size, must have been originally cast.
There are no records of this document before the 14th century, but at that time the plaque was in the Archbasilica of St. John’s in the Lateran, and was misunderstood by the tribune Cola di Rienzo to be an example of the strength of the Roman Senate and People in conferring power upon the emperor. In a letter written in 1350 to Arnošt of Pardubice, archbishop of Prague, Cola told the archibishop how he had the plaque set in the wall of the Lateran basilica. According to Cola, Pope Boniface VIII, had previously had it turned it upside down in order to hide the ancient inscription, and had used it as the top of an altar, perhaps to show his opposition to imperial power.
In 1576, Pope Gregory XIII donated what was then called the Tabula antiquae sanctionis (from the word sanctio, sanction, which introduces the last paragraph of the text) to the people of Rome, ordering it to be placed at the Capitol. It was first displayed in the Palazzo dei Conservatori. In 1733, Pope Clement XII had it moved to its present location on the Hall of the Faun.
The Latin text of the law is available at Epigraphik-Datenbank Clauss / Slaby. For the English translation of the law see M. H. Crawford (ed) Roman Statutes, I (1996), pp. 549—553, no. 39. These texts are also available from AncientRome.ru at this link.
Commune di Roma. The Capitoline Museums Guide (2013) 58.