Ratio and Proportion
This site presents a nice introduction to ratios and to proportions. There are some interactive problems.
http://www.purplemath.com/modules/ratio.htm

Ratio and Proportion
There is an interactive component to this site.
http://www.gomath.com/algebra/ratio.php

Euclid
Did you notice the Historical Perspective at the beginning of this section? Euclid is one of the most famous mathematicians from antiquity. If you want some additional information, you can check out this site.
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Euclid.html