Sextilis, the sixth month of the year that began in March, followed Caesar's July into imperial hands in 8 BCE, when the senate decreed that it should bear the name of Augustus. The decree, which the later writer Macrobius preserves, gave its reasons: in this month Augustus had entered his first consulship, celebrated three triumphs, and ended the civil wars with the fall of Alexandria, so the month was judged most fortunate to him and to Rome. Unlike the emperors who came after, whose renamed months died with them, Augustus had chosen a month genuinely woven through his own history, and the name held.
A famous story says he also lengthened it, stealing a day from February so that his month would not be shorter than Caesar's July. The tale first appears in the thirteenth century schoolbook of Johannes de Sacrobosco and modern scholarship rejects it: the old Sextilis of the republican calendar had twenty nine days, Julius Caesar's reform had already raised it to thirty one two decades before the renaming, and February's length was fixed by the same reform. The legend survives because it is tidy, but the calendar it describes never existed.
Roman August itself was a working month of harvest festivals: the Portunalia, the Consualia of the storing of grain, the Volcanalia of the twenty third when the destructive fire of the god Vulcan was asked to spare the full granaries, and the Opiconsivia of plenty at the month's end, a sequence that reads as one long negotiation with the gathered year.
Sources Religions of Rome, Volume 1: A HistoryMary Beard, John North and Simon Price with The Oxford Companion to the Year: An Exploration of Calendar Customs and Time-ReckoningBonnie Blackburn and Leofranc Holford-Strevens