Here's an image of a page from The Poissy Antiphonal that contains a hymn, in square note notation (at the bottom of the page), that begins Aurea luce et decore roseo - which was the original first line of Decora lux æternitatis, auream (and I believe this was the original longer hymn, as well):
Here is a snippet of the chant in modern notation from MMDB:
This page gives the Latin and English translation of Decora lux æternitatis, auream and says that:
First line of Original Text: Aurea luce et decore roseo. The hymn was considerably altered by the revisers under Pope Urban VIII, in 1632. Including both texts there are at least twelve translations. The complete hymn consists of six stanzas, including the doxology. The order of the stanzas in the complete hymn is as follows: Decora lux; Mundi magister; Beate Pastor Petre; Egregie Doctor Paule; O Roma felix; Sit Trinitati. Note the use made of parts of this hymn on the Feasts of St. Peter’s Chair (hymn 90), and of the Conversion of St. Paul (hymn 91).
Here is the English set of words to Decora lux æternitatis, auream, which I find quite wonderful, from Breviary.net:
With golden radiance bright, with fair and ruddy glow,
The Light of Light its beams o'er all the earth doth throw:
This holy-day, whereon to sinners hope is given,
The glorious Martyrdoms give joy to highest heaven.
Earth's teacher, and the guard of heaven's eternal gate,
True lights of all the world, earth's judges dread and great,
The sword-stroke, and the cross to them their victory give,
And now, with laurel crowned, in heaven's high court they live.
O happy city Rome, the precious life-drops shed
By these two noble chiefs thy walls have hallowed,
By nought that is thine own, but by their deeds of worth,
Thy fairness far excéls all beauty else on earth.
Now to the Trinity eternal glory sing;
All honour, virtue, might, and hymns of gladness bring;
He rules the universe in wondrous Unity,
And shall, through all the days of vast eternity. Amen.
Here, for comparison, are the words to Aurea luce et decore roseo at still another Google Book, Latin Hymns: With English Notes for Use in Schools and Colleges, from 1883.
From the other site, here is the page for Beate Pastor, Petre, clemens áccipe; Latin and English words are there.
The book Pange Lingua: Breviary Hymns of Old Uses with an English Rendering (a large PDF!), says of Felix per omnes festum mundi cardines (the hymn itself is found on page 52 by page number of that document) that:
"This hymn was sung at First Vespers of SS. Peter and Paul according to the use of the Church of York, which was followed of old throughout the north of England as that of Sarum was in the south. The seventh verse, in a slightly altered form, now forms part of the Breviary Vesper hymn for the feast, and the fourth and fifth verses are also retained in the Breviary for use on the lesser feasts of St. Peter."
So I think we might find this one listed in the Anglican Breviary; the ones above are obviously from the Roman one.
Interestingly, two of the above hymns were written by a woman, according to Wikipedia:
H. Elpis, wife of Christian philosopher poet Anicius Manlius Severinus Boethius, wrote the lyrics to two hymns for the feast of St. Peter and Paul: "Aurea luce et decore roseo" and "Felix per omnes festum mundi cardines".
Fr. Stephen Gerth of the Church of St. Mary the Virgin writes of this feast that:
Early Christian tradition records the memory that Peter and Paul were martyred in Rome under Nero, who began a systematic persecution of the Christian community there after the famous fire in A.D. 64. We know little about the first Christians in Rome other than that there were many martyrs. I believe it is correct to say the historical record suggests the local church in Rome was one where the tradition of a single bishop for the city emerged after a period when there was a council of bishops. For those interested in a history of the Papacy, I highly recommend the very readable The Conclave: A Secret and Sometimes Bloody History of Papal Elections (Rowman & Littlefield Publishers, Inc., 2003) by Michael Walsh, a Roman Catholic historian.
It is very hard to write about Peter and Paul because it is so, so easy to use Christian language and thought of the succeeding generations to describe the lives and work of the first generations. No one who lived while Peter lived thought he was the "pope" - the title was not used for the bishop of Rome until the fourth century. In the Acts of the Apostles, although Peter spoke and was present, it was James of Jerusalem, the brother of our Lord, who gives the judgment of the "apostles and elders" on the question of the customs gentiles who became followers of Jesus Christ were to follow. Clearly, like Paul and others, Peter was an "apostle." It is not clear at all that anyone thought of apostles as bishops. The word "bishop," that is, "overseer," is used in the New Testament. What it meant then and what it came to mean are very different things.
That said, there are, of course, some excellent reasons for the Church to celebrate Peter and Paul. Peter knew Jesus, was one of the Twelve, is first to confess Jesus as Christ, and in general takes on a very active role in the Gospel accounts and in the Acts of the Apostles. He betrayed Jesus before dawn on the day Jesus was crucified but also went to the tomb on the first Easter Day. He knew the Risen Lord and became one of the leaders of the first community of Christians in Jerusalem. There is no reason to doubt the tradition of his martyrdom and Paul's martyrdom in Rome and to have the highest reverence for their life and death.
Paul knew and persecuted the first Christians in Jerusalem. The Risen Lord appeared to him and called him to be an apostle. The earliest books of the New Testament are his letters, not the gospels. After Luke, he is the second principal author of the New Testament. The power of his teaching and preaching remain; the power of the Holy Spirit in his life remains. About his apostleship, he wrote, "We are fools . . . We are weak . . . we have become, and are now, as the refuse of the world, the offscouring of all things" (See 1 Corinthians 4:9-16).
St. Augustine wrote, in Sermon 295, that:
Both apostles share the same feast day, for these two were one; and even though they suffered on different days, they were as one. Peter went first, and Paul followed. And so we celebrate this day made holy for us by the apostles' blood. Let us embrace what they believed, their life, their labors, their sufferings, their preaching, and their confession of faith.
Here's the SS. Petri et Pauli page at Medieval Music Database. And here are the chant propers for the mass, from the Benedictines of Brazil. Here is an mp3 of the Offertory hymn, Constitues eos; below is the chant score. The English translation is: "You will make them princes over all the earth; they will remember your name, oh Lord, in every generation."
For some reason, I really like this El Greco of Peter and Paul:
But then, I like this icon, too: