Work in pairs. Read and say how old the ancient Greek theatre is. Since we all live in AD or CE (Common Era) years now, there is no need to say "AD", it is understood. So, it is 2020 AD, but all that you say is 2020. If you have a date in BC or BCE (Before Common Era) and you want to find out how long ago it was, you just add it to the current year. So, if we want to know how long ago 1000 BC was, it was 3020 years ago (2020 + 1000 = 3020).