In addition to the propers and antiphons appropriate to the respective festivals of the church year, the second part of the 1607 Gradualia contains, it is thought, a hidden tribute: a set of Propers for the Feast of St. Peter’s Chains, perhaps celebrated on 1 August 1603 to commemorate, on 21 July of that year, the elevation to the peerage of Byrd’s longstanding patron Sir John Petre.