So strange you mention Petra
Ended up there on a dig on Palmyra/Temple of Baal
Interesting the Romans called the area Arabia Petraea, made me think of David Petraeus
But when you think about time and how it relates to Jesus
BC means before Christ
AD means anno domini, or "in the year of our Lord", used after they killed Christ
Domini, as in dominate
AD = After they "dominated" Jesus
Then look at Dominion
Etymology is fun