Augustus
The first Roman emperor, who took the name Augustus in 27 BCE. He corrected the priests' error in the leap years, and the month Sextilis was renamed August in his honor in 8 BCE.
63 BCE – 14 CE
How the Romans fixed the year
Censorinus, On the Birthday 20–22 (238 CE), in the edition of Friedrich Hultsch (Leipzig, 1867) · 238 CE
ex his duodecim mensibus duorum tantum nomina inmutata. nam Quintilis Iulius cognominatus est C. Caesare V et M. Antonio cons. anno Iuliano secundo: qui autem Sextilis fuerat, ex SC. Marcio Censorino C. Asinio Gallo cons. in Augusti honorem dictus est Augustus anno Augusti vicensimo. quae nomina etiam nunc ad hanc permanent memoriam.
Of these twelve months, only two have had their names changed. Quintilis was renamed Iulius [July] when Gaius Caesar, for the fifth time, and Mark Antony were consuls, in the second Julian year. The month that had been Sextilis was renamed Augustus in honor of Augustus by a decree of the senate. That was when Marcius Censorinus and Gaius Asinius Gallus were consuls, in the twentieth year of Augustus. These names have lasted to our own day.
Where the months got their names
Macrobius, Saturnalia 1.12–14 (early fifth century CE), in the edition of Franz Eyssenhardt (Leipzig, 1893) · early fifth century CE; the dialogue is set in the 380s
Augustus deinde est, qui Sextilis antea uocabatur, donec honori Augusti daretur ex senatus consulto, cuius uerba subieci: cum imperator Caesar Augustus mense Sextili et primum consulatum inierit, et triumphos tres in urbem intulerit, et ex Ianiculo legiones deductae secutaeque sint eius auspicia ac fidem, sed et Aegyptus hoc mense in potestatem populi Romani redacta sit, finisque hoc mense bellis ciuilibus inpositus sit, atque ob has causas hic mensis huic imperio felicissimus sit ac fuerit, placere senatui ut hic mensis Augustus appelletur. item plebiscitum factum ob eandem rem Sexto Pacuuio tribuno plebem rogante.
August comes next. It was called Sextilis until a decree of the senate gave it in honor of Augustus. Here are the decree's words: "Whereas the emperor Caesar Augustus, in the month of Sextilis, entered on his first consulship and brought three triumphs into the city; and the legions were led down from the Janiculum to follow his command and his cause; and in this month Egypt was brought under the power of the Roman people, and in this month the civil wars were ended; and whereas for these reasons this month is and has been the most fortunate for this empire, the senate resolves that this month shall be called Augustus." A law of the people was also passed for the same purpose, on the motion of Sextus Pacuvius, tribune of the people.
hic error sex et triginta annis permansit, quibus annis intercalati sunt dies duodecim, cum debuerint intercalari nouem. sed hunc quoque errorem sero deprehensum correxit Augustus, qui annos duodecim sine intercalari die transigi iussit, ut illi tres dies, qui per annos triginta et sex uitio sacerdotalis festinationis excreuerant, sequentibus annis duodecim nullo die intercalato deuorarentur.
This error lasted for 36 years. In those years twelve days were inserted, when there should have been nine. This error too was discovered late, and Augustus corrected it. He ordered twelve years to pass without an extra day. In this way the three surplus days, which had piled up over 36 years through the priests' haste, would be used up in the next twelve years with no day inserted.