Julius Caesar moved to a solar calendar with 12 months to better track the seasons compared to the 10 month Lunar calendar. Naturally he got a month (July) named after himself. August would come later (named after Augustus Caesar, his adopted son). The months that were added however were actually January and February (the calendar year used to end in December and start with March. July was Quntilis (5th month) and August Sextilis (6th).