Today we see heaps of buildings having their year of construction displayed on their front. When did this start to become common? I'm assuming it would be a Christian church (with Jesus being the start of our current calendar).
It's probably not the first, but the Pantheon in Rome has its date above the portico "Marcus Agrippa, son of Lucius, Consul for the third time built this"- which means it was built in 27BC in our calendar according to the List of Consuls. The Romans commonly dated things that way.
(The current building though is actually a replacement of the 27BC one, built about a hundred years later).
I expect there'll be earlier Roman examples- does anyone know if Greek. or even Egyptian buildings are dated like that?