“Writing this paper has been a tedious work … Still I feel it had to be done”: thus begins R. Krautheimer in an article which remains the best discussion of the issue of how to date the Basilica of St. Peter. Now, a quarter of a century later, the topic must be revisited. Although there are some updates, there is little really new to report, but Krautheimer’s study is not as widely read as it should be, even remaining unknown to many scholars who have dealt with the topic in the meantime (perhaps because it was published in a journal specializing in art history). Even if the result will be no less tiresome, it is even more necessary than it was in Krautheimer’s day.