These walls are called "serpentine" because they run a sinusoidal course, one that lends strength to the wall and allows for the wall to be only one brick thick, one of many innovations by which Jefferson attempted to combine aesthetics with utility.
http://en.wikipedia.org/wiki/University_of_Virginia
http://agoraphilia.blogspot.com/2006/03/jeffersons-wall-take-two.html
