After his decisive victory over Marc Antony and Cleopatra in 33 BCE, the now uncontested emperor, Augustus Caesar, decided he should have a month named after him (July was already named afer his great uncle, Julius Caesar). Due to his successful military campaigns during what is now known as the month of August, the Roman senate agreed to name the month after the reining emperor. However, since, August only had 30 days, not to incinuate that their emperor was in any way inferior, the senate took a day from February's 29. (Back then, the calendar year began March 1st and alternated between 31 and 30 days (except for February which got the remaing 29.) Then they had to flip the number of days in the remaining months around to not have three 31 day months in a row. Seems like a lot of work!
Nathaniel Grauwelman as well as various staff and volunteer writers.