Holly is another popular symbol and decoration for Christmas.     
The Druids thought it was blessed by the sun because it stayed green all year.  They considered it sacred. 
The Celts thought holly branches placed around windows and doors would trap evil spirits trying to enter the house.
The Romans gave holly to their friends during Saturnalia as good luck charms and protection from evil.
Holly is one of the trees said to have provided the wood to make the crucifix of Jesus.  According to one legend, the holly berries were white until the crucifiction of Jesus, then they turned red.  Another legend says the leaves with the points that resemble thorns symbolize the crown of thorns placed on Jesus.  And, since it is an evergreen, it is also a symbol of eternal life.