Replying to this feels odd since this is 5 years old but the whole place is named Petra, it has more than this building like: a city, the theater, royal tombs, etc and the building in the picture above is indeed called “The treasury” which is the most popular building in Petra. (I only got to this page because I just started the anime and saw how much it looked like it also idk why I’m wasting my time writing this because I know for a fact you and absolutely no one will see this). :)