It is a Solemnity in the Sacrosanct Basilica of St. Peter today, for today is the anniversary of its dedication in 1626.
The Basilica has its own Proper for various days of the year. Here is the Collect for today’s Solemnity:
Deus, qui beati Petri Apostoli dignitatem
praecipue in nostra sacrosancta basilica facis esse gloriosam,
ut et doctrina semper ipsius foveamur et meritis.
Dignitas, is "dignity", of course, but also "moral importance" in liturgical prayers. For Apostles, this word is used to underscore their role in the Church precisely as Apostles.
O God, who are now making glorious
the dignity of the the blessed Apostle Peter,
especially in our most holy basilica,
grant, we beseech You,
that we may be supported both by his teaching and by his merits.
An old photo for this blog, but a good one.