History of Philosophy: The Skeptics and Roman Eclecticism

Sources: 

The History of Philosophy: Founders of Western Philosophy, Thales to Hume by Leonard Peikoff   http://www.peikoff.com/courses_and_lectures/the-history-of-philosophy-volume-1-%E2%80%93-founders-of-western-philosophy-thales-to-hume/ 

The Classical Mind by W.T. Jones.  http://www.amazon.com/Classical-Mind-History-Western-Philosophy/dp/0155383124# 

Great Minds of the Western Intellectual Tradition  http://www.thegreatcourses.com/courses/great-minds-of-the-western-intellectual-tradition-3rd-edition.html