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What was the Lex de Imperio Vespasiani?

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Vespasian Bust of Vespasian, found at Ostia; in the Museo Nazionale Romano, Rome.

The Lex de Imperio Vespasiani (Law Regulating Vespasian’s Authority) was a significant piece of legislation passed on December 22, 69 CE, by which the Senate conferred imperial powers upon Vespasian en bloc. The act was subsequently ratified by the Assembly.1

This law is historically notable for several reasons:

Precedent: It is believed to be the first time such a comprehensive law was passed to grant imperial powers, as previous Julio-Claudian emperors had not sought explicit sanction for all their authorities in this manner.21
Content: A fragmentary copy of the law survives and is preserved on the Capitol in Rome. Scholars have noted that the text includes provisions that effectively conferred a naked autocracy upon the emperor.12
Context: The legislation served to formalize Vespasian's position following the civil wars of 69 CE, providing a legal framework for his rule, even though he remained frank about the military origins of his power.21