Art History Timeline: Pairs essays and works of art with chronologies, telling the story of art and global culture.
Smarthistory: Art History on Khan Academy is a collaboration of art historians, archeologists, curatorswho want to make the highest-quality art history learning content freely available to a global audience. Includes videos and written materials.
Wikipedia's most important role is to provide an introduction to the subject. It perfect for preliminary research and when you want just the facts.
There is much to know and there is an entire guide devoted to WIKIPEDIA.