More specifically on Roman culture, history, technological breakthroughs, etc. Most of the documentaries I find focus on Roman conquest.
Please look at "ancient rome: rise and fall of an empire" documentary series by BBC. it contains 6 episodes: Caesar, Nero, Judean Rebellion, Gracchus Reforms, Constantine and Barbarian Invasion. http://www.imdb.com/title/tt0864944/?ref_=nm_flmg_act_38