[null and void]

When the date is after Christ's birth, the "A.D." precedes the number, e.g., A.D. 43 = "In the year of Our Lord (anno domini), 43."

In the first millennium, the year was often preceded by an I, since Jesus was spelled Iesus, following Ancient Greek Ἰησοῦς (Iēsoûs) since the letter J didn't gain currency until the 1500s.

Old building had cornerstones with the date in this format, e.g. a building erected in 347 A.D. would be marked I347.

Which caused an apparent missing millennium in construction, as it was read as 1347, and therefore it looked like nothing survived from before 1000 A.D.

[Verginius Rufus]

In A.D. 347, the Anno Domini system of dating had not yet been invented. So no one would have used it--and they would not have used Arabic numerals on a cornerstone. If they tried to date it they would have counted from the foundation of Rome (753 B.C.) or used the names of the consuls of the year.