On March 25, 1436, a great procession wound through the streets of Florence. Church prelates, led by Pope Eugenius IV himself, and the Signoria of the Italian city-state, led by Cosimo de' Medici, marched with ranks of musicians along a ceremonial wooden bridge from the steps of Santa Maria Novella to the newly completed Cathedral, Santa Maria del Fiore. There the Cardinal of Venice would offer Mass and the Heir of St. Peter would officiate in the liturgy of Dedication. For the Cathedral of Florence, the "cradle of the Renaissance," Ghiberti crafted her Baptistry's bronze "Doors of Paradise," Luca della Robbia and Donatello carved her cantoria. Filippo Brunelleschi had now crowned her with a momumental dome. And for the event, the director of the Papal choir, Guillaume Dufay, presented new compositions, including the celebratory isorhythmic motet Nuper rosarum flores. The text, probably written by Dufay himself, consists of four Latin stanzas, seven lines of seven syllables each. It addresses St. Mary of Flowers, as she was known in Florence, offering the church to her and asking for her perpetual intercession for her Florentine people. The upper two voice parts (often dividing for further harmonic richness) sing this text in four sections, each beginning with a duet of 28 breves' duration and concluding with 28 breves of music for all four voices. The upper melodies are free-flowing and rhythmically active, though melodic fragments are recycled later in the piece (a technique known as isomelism). One exceptional moment in the counterpoint occurs when the text mentions the name "Eugenius": the texture suddenly clarifies, so that the Pope may be gratified to hear his own name sung. The fourfold structure of the motet derives from the isorhythmic plan of the lower voices, which sing a long-note cantus firmus in canon with one another. Their melody and text is a plainchant: "Terribilis est locus iste," from the liturgy for the Dedication of a Church. Specifically, Dufay uses the first 14 notes of this famous chant. Then the lower voices sing their melody in four different rhythmic configurations, by the application of different mensurations to each section. This results in a durational ratio of 6:4:2:3. While the compositional device of isorhythm was common in the fifteenth century, especially for large occasional pieces, Dufay's choice of ratios here is unique for its complexity. In a famous article, published in 1973, Charles Warren argued that this unique set of ratios corresponded to the large-scale architectural dimensions of the Cathedral—nave, crossing, apse, and dome. This theory was later challenged by musicologist Craig Wright, who, nevertheless, further elucidated the presence of carefully crafted numerology in Dufay's composition. The unique isorhythmic ratio chosen to honor the Florentine Cathedral may symbolize instead the Old Testament Temple of Solomon, whose overall length, length of nave and sanctuary, and height were 60:40:20:30 cubits. The number seven—crucial to the sectional divisions and to the structure of the poem—relates to the seven pillars of the Temple, the sevenfold gifts of the Holy Spirit (which filled the Temple at its dedication), and the seven censings of the altar in the Dedication service. The Temple symbolism is then overlaid with Marian meaning, as seven signified the Virgin Mary's perfection: seven joys, seven sorrows, seven feasts. The Virgin, whose womb was the temple which nurtured the incarnate Christ, is richly honored in the symbolic language of her Florentine temple's dedication.

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