July from Julius Ceasar.
August from Augustus Ceasar.
Romans added 2 months to the original Greek/Egyptian calandar to better match the phases of the moon. The problem was that the traditional new year was way off the original concept of the death/rebirth of the sun, the shortest day.
The calendar was yet again changed by the Catholic Church in the 17th centuary, by adding the concept of the leap year.
This caused great consternation in the populace as people thought that the Church had lopped off 11 days from their lives.