Throughout recorded history the rose has been valued for it's beauty and scent.  It has also been revered for it's symbolism.  The modern rose originated in Persia and was very popular in ancient Egypt but fossil roses have been found that date from 32 million years ago.  Roses are mentioned in the Song of Solomon and the book of Isaiah in the Bible indicating that it was a sacred symbol even then.  At various times and in various circumstances, it has a number of meanings.  Roses can symbolize purity or heavenliness, especially white ones.  It can symbolize transmutation, completion or achievement, particularly in reference to spiritual development.  Of course it is best known as a symbol of love.  The catholic style prayer beads got the name rosary because in early versions, the beads were often dried rose buds.  The rose was a symbol of the goddess Venus but also symbolizes the blood of Christ.  The Rosicrucians get their name from the rose cross, a cross with a rose in the center, which is their symbol.  The rose is also a symbol of Mary, mother of Jesus, as indicated in this quote from Dante's Paradiso:

"Why are you so enamored of my face that you do not turn your gaze to the beautiful garden which blossoms under the radiance of Christ? There is the Rose in which the Divine word became flesh: here are the lilies whose perfume guides you in the right ways." 

    One odd use of the rose as a symbol is when it symbolizes silence or secrecy as in the expression "sub rosa" which literally means "under the rose" but actually means "in secrecy".  I suspect this idea originated with early Gnostics, mystics and mystery schools that kept much of their teachings secret.  In some such organizations, a rose was hung from the ceiling during meetings to indicate that what was being discussed was private.
    In numerology, the number of the rose is five because the wild rose has five petals and modern roses have multi-layers of petals each layer having five petals.  The number five is symbolic of health and safety.  

Roses in myths and legends:

It is claimed that once, when Julius Caesar arrived to dine with Cleopatra, she had the floor of the dining hall buried two-feet deep in roses.

There is a long-standing legend about a secret organization called "the Sisterhood of the Rose".  The sisterhood is said to be twelve women of special talents who work for the betterment of mankind.  It's existence has never been proved.

The rose windows in Notre Dame cathedral, Chantres cathedral and others from the same time are very mysterious.  the exact symbolic meaning of them is unknown.  Also, the method of staining the glass used has been lost.  When a piece gets broken and has to be replaced, the difference is obvious.  Modern stained glass makers cannot duplicate the depth and richness of the color.

Roman legend says the beautiful maiden Rhodanthe was turned into a flower by the jealous goddess Diana thus creating the rose.

The Greek legends say it was Aphrodite who name the rose.

Ancient clay tablets found in the temple of Ur in what is now Iraq indicate that the sultan of Baghdad back then used 30,000 jars of rose water a year to make the rooms used by his harem smell good.