Smarthistory has a number of excellent articles and videos about the history of art. No matter what you are researching, this is a great site to check as their information deals with diverse cultures and time periods. For example, at the time I’m posting this, the first two topics on their landing page deal with the ancient Mediterranean and Modernism. I highly suggest you check this out.
Website: Smarthistory: The Center for Public Art History
Humanities Scholars 