Columbia University Guide to Ancient Architecture
http://www.learn.columbia.edu/ha/html/ancient.html
Columbia University Interactive Guide to Architecture
http://www.learn.columbia.edu/ha/html/renaissance.html
Columbia University Guide to Baroque Architecture
http://www.learn.columbia.edu/ha/html/baroque.html
Columbia University Guide to 19th Century Architecture
http://www.learn.columbia.edu/ha/html/19c.html
Columbia University Guide to Modern Architecture
http://www.learn.columbia.edu/ha/html/modern.html