The rosary is a form of combined prayer and meditation that has been around for over 1,200 years. The origin of the rosary dates back to the ninth century when Irish monks would recite and chant the 150 Psalms of the Bible as a major part of their worship. People living near the monasteries were drawn towards this beautiful and harmonious devotion, and they became very eager to join in with the monks' prayers.
Unfortunately, the people were not able to adapt to this form of prayer because the psalms were very hard to memorize and printed copies of the psalms were not readily available. As a result, it was suggested to the people outside the monastery that they recite a series of 150 "Our Father" prayers in place of the psalms.
This innovated version of the rosary was widely spread by the divinely inspired works that St. Dominic who focused on the life of Jesus through the mysteries of His life. The prayers of the Rosarium were later broken out into sets of 10 and these groupings became known as decades. Each decade of ten "Hail Mary" prayers would be preceded by one "Our Father".
As you can see, the rosary we know today is the result of many evolutions dating back several hundred years. Although the manner in which the rosary is recited has changed, the results of praying the rosary are still the same. Countless interventions still occur today, and the power and divine graces the rosary offers are available to everyone who is willing to give it a chance.