In former days, stained glass windows were looked upon as ‘Books of the poor and illiterate’. These pictures helped people to learn of the scriptures and the lives of the saints and doctrines of the church. Though this is no longer so, such is the craft of the designs that we can learn much, and be reminded of so much of value, simply by looking and thinking upon what we see when we look through the window. The stained glass windows of St Peter’s are largely responsible for the special atmosphere created in the church. Richness of colour and delicacy of design combine to make the windows some of the best of their kind in the country. Installed after the turn of the last century, the windows come from two main sources – the three large windows on the sanctuary, the window in the Sacred Heart Chapel and the large window in the repository were made by the famous firm, Meyer of Munich, at a cost of £160 each! The windows in the nave are the work of Hardman of Birmingham. These have less vibrant colours but are stll a fine example of the stained glass makers craft.
The 'Presentation' window on the Sacred Heart side shows the scene in the Temple when Mary and Joseph took the child Jesus to consecrate Him in the service of God as their first-born male child. With them are Simeon and the prophetess Anna and the window shows the text of Simeon, "Behold, this child is set for the rising and falling of many in Israel." At the top of the window, a high Priest is shown bearing a scroll which reads, "In this place I will give peace". The window was erected in memory of John Hayes, who died on 20th December 1909, by his wife Mary.
The third window on the Sacred Heart side shows "Christ's Commission to Peter" quoting the text "Thou art Peter and upon this rock I will build my Church." Peter, as so often, is depicted holding the keys of the Kingdom....the power of the Keys. He is shown again in the top wlndow, this time in full Pontifical Vestments, with the inscription, "Tu Es Petrus" (You are Peter). The window commemorates the death of Everilda Turnbull on the 23rd March 1893.
In the porch of the church is a window depicting St John Lloyd and St Philip Evans who were martyred in 1679 at the junction of Crwys Road and Richmond Road in Cardiff.
The current repository was originally the church's baptistry and the window depicts the baptism of Jesus by John the Baptist.
On the south side of the church the first window is that of the Nativity and shows a traditional nativity scene with the angel bearing the glad tidings of Christ's birth.
The Sacred Heart Chapel: St. Bernadine with the text "My God and My all" and St Helen who carries the relic of the True Cross which she is said to have found at Jerusalem.
The fourth window on the Sacred Heart side depicts the Last Supper and shows Judas in the background, about to leave the Upper Room with his money, while the other disciples are gathered around the central figure of Christ. "I will move all nations and the desired of all nations shall come". The person at the top is the mysterious figure of Melchisedech who came to Abraham with gifts of bread and wine but who was given no ancestry: his priesthood is eternal. The window is in memory of Alderman Patrick William Carey who died on 4th June 1910.
The next window on the Sacred Heart side is “The Carrying of the Cross” – the Via Crucis – and shows the traditional but not scriptural incident of Jesus being met by Veronica (on the left) who wipes His face with a towel and is left with an imprint on the towel. The other figures are Our Lady, St John and Mary Magdalene. The window bears the words, “He hath borne our sorrows and carried our infirmities,”The small window at the top shows Christ after the scourging and Pilate's words: "Ecce Homo" (Behold the man). Fr Fortunus Signini, who died in 1889, is commemorated by this window. The window was given by Alderman P W Carey, JP and his wife to Fr Signini’s memory..
The last window on the south side shows the Trinity in glory with the three figures of Father, Son and Holy Spirit in their traditional forms. The text reads: "There is one Mediator of God and men, the man Jesus Chrlst, who gave hlmself, a redemption for all. Jesus shows His wounds to His Father, interceding for our salvation."
The last window on the North side shows 'The expulsion from Paradise' and bears the promise made immediately after the Fall "I will put enmity between thee and the woman, and thy seed and her seed." Our Lady and her child are shown at the top of the window: Mary as the woman of the Book of the Apocalypse clothed with the sun, standing on the moon and with a crown of twelve stars. She is crushing the head of the serpent (Satan) which is the only way to kill a snake. They are thus the fulfilment of the first promise of salvation.
The Sacred Heart Chapel: St John and St Patrick (to the glorious apostle of Ireland from one of his children) .
The window on the left of the Sanctuary shows the event from the Acts of the Apostles when St Peter is released from prlson by the angel who struck him on the side and led him out, the chains falling from his hands. The tradition of St Peter's death is shown above that - death by crucifixion, but out of humility and reverence for Jesus he asked to be crucified upside down. In the botton window we see St Patrick preaching to the court of King Laoghaire at Tara. This window was donated by the Parishioners of St. Peter's, the central window by Fidele Primavasi and the window on the right by John, Marquis of Bute.
The central window on the sanctuary shows Jesus teaching the crowds from St Peter’s boat; this is why the church is sometimes referred to as the Bargue of Peter. Beneath this is a representation of Pope St Gregory sending St Augustine and his companions to preach the faith to the English. At the top in the centre is the commission of St Peter: "I will make you a fisher of men."
The window on the right of the Sanctuary shows St Peter addressing the first Council of the Apostles and below this Pope Eleutherius is shown commissioning St Fagan and his companion preachers to Wales (although there is some doubt about this in historical terms.) Above that window is the 'Quo Vadis' window depicting the legend about St Peter leaving Rome at the time of persecution and meeting Jesus on the Appian Way and asking him: Quo vadis, Domine? (Where are you going, Lord?) Jesus is said to have replied: I am golng to Rome, to be crucified again. Peter took the hint and returned to Rome where he was himself eventually crucified.
In the Lady Chapel there are two small windows showing the figures of the parents of Our Lady: St. Joachim and St. Anne. The Children of Mary donated these.
The windows on the north side of the church depict mysteries of Our Lady's life, while those on the south side are of the life and death of Jesus - although the two obviously intertwine very often. The window nearest the Lady Chapel is of the intercessary power of Our Lady who is shown interceding with Jesus who shows his love in the Sacred Heart. It bears the text "Oh, King, give me my people for whom I plead" which sums up Our Lady's role of intercessor before the throne of God. Above is a representation of humility. This window was created by Hardman and is in memory of Mary Stone.
The second window on the north side depicts the Marriage Feast at Cana and the text, "What wilt thou, Queen? What is thy request?" Above this group is a symbolic figure of the Church with the text "Ecce Ecclesia" (Behold the Church). The window is an offering of love and thanksgiving from Thomas Joseph and Edith Elinor Callaghan.
The Visitation window has the text from St Luke "Henceforth all generations will call me blessed" and shows the meeting between Mary and Joseph and Elizabeth and Zechariah, parents of John the Baptist.
The fourth window on the north side tells of the Annunciation “Be it done unto me according to thy word”. At the top is the figure of the prophet Isaiah who foretold the incarnation with the words "A Vlrgin shall conceive and bear a Son and shall call Him Emmanuel" The window is in memory of Thomas Callaghan who died Oct 10th 1899 and of Sarah his wife, Feb 2nd 1905.