Did a year have 12 months in BC?

Yes, a year had 12 months in BC, similar to how it does today. The Roman calendar, which was in use during much of the BC period, originally had ten months but was later reformed to include twelve months. The Julian calendar, introduced by Julius Caesar in 45 BC, established the 12-month structure that continued into the modern Gregorian calendar. Thus, the concept of a 12-month year was well established by that time.