Ever since at least the time of Constantine, when the persecution of Christians ended and the first Basilica on Vatican Hill, on top of the tomb of the Prince of the Apostles, was built, the highlight of the pilgrimage made by uncountable numbers of priests "ad limina apostolorum" has been the possibility of celebrating a personal private Mass at Saint Peter's. This has continued unabated even after the Novus Ordo.
Also, ever since at least the time of John Paul II (in the crypt), and more freely since Benedict XVI above ground, the Traditional Latin Mass has been celebrated privately in the Basilica.
But those venerable practices may be about to be abolished.
