Have you ever wondered why February is shorter than other months?
Back in the early days of the Roman Empire their calendar year started with the first month of Spring. That's March, which was named after Mars, their god of war. That month had 31 days and the rest of them alternated between 30 and 31 days until the end of the year. The last month, February, only had 29 days.
The Romans realized the year is slightly longer than 365 days, so an additional day was added to February every fourth year.
And, eventually, they changed the first month to January.
When Augustus became the Caesar, or emporer he wanted his month, August, to be as long as the month named after his predecessor, Julius Caesar. (Julius Caesar's month was July.) It was supposed to be lucky for a month to have an odd number of days. So Augustus had one day taken from the last month of the year and added to August.