Complex sentence: Year 339 BC was a year of the pre-Julian Roman calendar.In the Roman Empire it was known as the Year of the Consulship of Mamercinus and Philo (or, less frequently, year 415 "Ab urbe condita").
Split into simpler sentences: Year 339 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Mamercinus and Philo (or, less frequently, year 415 "Ab urbe condita").