Some people believe Saint Dominic to be the initiator and promoter of the rosary, and that he had received the rosary from Our Lady.  In fact, it was Dominic of Prussia and Alanus de Rupe who were the actual pioneers of the rosary prayer.  This happened in the fifteenth century.

Dominic the Carthusian (St. Alban, near Treves, about 1410) promoted a rosary of fifty Hail Marys and 50 Vita Christi clauses.  The clauses were references to the life of Christ (e.g., the conception by the Holy Spirit) added to the Aves.

Alain of Roche (or Alanus de Rupe, second half of the fifteenth century, Dominican, Douai/France) established a brotherhood of the rosary (Confraternity of the Psalter of the Glorious Virgin Mary, around 1470) which was instrumental in disseminating the rosary throughout Europe.  Jacob Sprenger founded around 1475 an even more famous one in Cologne.  Alain's rosary consisted of 150 Aves reflecting the Psalter, and was subdivided in three groups of fifty each, following the three fundamental mysteries of Christ's Incarnation (Joyful mysteries), Passion (sorrowful mysteries), and Resurrection (Glorious mysteries).  Alain rejected Dominic's shortened version of the rosary (50 Aves), and likewise, rejected the name "rosary."  His name for the rosary prayer was the "New Psalter of the Virgin," highlighting thus that the rosary had 150 Aves, not only fifty, just as the Psalter numbers 150 Psalms and not fifty.  His opposition to the name "rosary" stems from the "vain and worldly" origins of "rosarium," "corona," or "sertum."

The "rosarium" or rosary indeed has pre-Christian origins. Ancient Rome celebrated the "rosalia," a spring festival commemorating the dead.  In Greek tradition, the rose was Aphrodite's flower.  It reminded one of the blood of the gods.  Venus, Aphrodite's Roman counterpart and protector of love, is frequently pictured with a wreath of red and white roses, or holds a rose in her hand.  Similarly, from ancient times to the middle ages, the ideal place for romantic encounters were "rose-gardens," that is, gardens protected by a rose hedge.  The expression "rose-garden" has a wide variety of meanings, from libertine to more edifying usage.  It is, together with "rosenkrantz" (wreath of roses), best known for its role in literature of profane romance (see, e.g., Roman de Ια Rose, early, thirteenth century).

It is well-known, however, that the symbolism of the rose has a long history in Christian tradition.  The rose was frequently applied to Mary, sometimes to Jesus himself.  This is true for patristic texts, (e.g., Ambrose, Sedulius), Latin hymns, and sequences (De gaudiis B. Mariae, fifteenth century).  Mary is "God's rose-garden" in Latin hymns, whereas Dante lauds her as the "Rose in which the word of God became flesh" (Paradiso, 23:73-74).  It is in the context of this literature using the symbolism of the rose that we have to search for the origin of the word "rosary," in Latin, rosarium.  The evolution and usage of the word happened in stages.

1. "Weaving a chaplet for the Virgin Mary" (Gregory Nazianzus, 4 c.).  The word chaplet has the meaning of wreath (corona) (Esser.)
2. " A chain of fifty Aves" (early l3 c.)  Beguines of Ghent prayed three such chains daily.  The terms used are "corona" or "sertum
."
3. "Aves seen as Roses" (late l3 c. legend in Latin, Catalan and German versions).  According to the legend, the Hail Marys recited by a monk became roses and or a rose garland in the hands of Mary (see text in annexe below!)  The early Latin versions of this legend use "corona" (crown) and "sertum" (wreath) for garland.
4. In German versions of the same legend from l2/l3 c., the rose garland of  "Aves seen as Roses" is named "Rosenkranze," and subsequently was retranslated into Latin as rosanum, our rosary.
5. Up until that time, the term rosarium was used in the sense of florilegium, a bouquet of flowers designating a collection of anecdotes, texts, or prayers.
6. Now rosarium or rosary is used to characterize spiritual gifts offered to the Virgin.  Little by little, the expression "psalterium" merges with rosarium.  In Engelbrest of Admont's (1279-1331) Psalterium B. V. Mariae, each of the 150 advocations begin with Ave, rosa. (Deves, Blume).
7. We previously mentioned the controversy between Alanus and Dominic over the words rosary or psalter.  Some authors in subsequent centuries used both expressions (Adam Walasses, 1571).  Latin languages gave preference to "serto" or "capelleto."  The papal bull of 1478 used the term "rosario."  Jacob Sprenger's German rosary manual of 1476 also used the word rosary.

It is the attractiveness of the rose symbolism that tipped the balance.  Part of this attractiveness lies in the ability to combine and associate profane and spiritual meanings.  In particular, it was the assimilation of the Ave Maria (Hail Mary) to the Rose (Aves as Roses), and the 150 roses to the rose garland that made the term rosary very popular.  The Ave Mary is a rose.  It is made up of five sentences, and so has five petals that represent, according to Our Lady Mary's Rose Garden, the letters MARIA (64-65; 190-191).  

Annexe: The legend of the Aves that became Roses

A good, simple, secular man had the custom of making every day a chaplet of roses, or flowers, or rue, or of whatever he could, according to the season, and placing it on the head of an image of Our Lady.  This he did with great enjoyment and pious devotion.  The Virgin saw the good intention of his heart and, wanting to help him further it, gave him the desire to take up the religious life.  And so he became a lay brother in a cloister.  But in the cloister he was given so many tasks to perform that he no longer had time to make Mary her chaplet as he was accustomed to doing.  Because of that, he became dissatisfied and was about to leave the order and go back into the world, when an older priest became aware of his distress.  The priest wisely advised him that he should recite each day fifty Ave Marias in place of the chaplet and convinced him that Queen Mary would prefer that to all the rose chaplets that he had ever made.  The lay brother followed the advice and continued in it for some time.

Then the brother rejoiced from the depths of his heart, and, from that day forward, made a spiritual rose chaplet of fifty Ave Marias for Queen Mary daily and instructed other good people in the practice.  In this manner, the rosary was created and made known to us.  And one may believe that the robbers bettered their lives as a result, because God's grace had permitted them to behold the Mother of Mercy .

(Dominic of Prussia, Wie der Rosenkrantze ist funden, in: B. Winston-Allen, Stories of the Rose,
1997, 100/101)