What is the symbolism of the 13 stripes on the American flag?

The flag of the United States of America, like all national flags, is laden with symbolism. A version of the current American flag was adopted in 1777, and although the number of stars has since changed, the design has remained largely untouched. The symbolism of the colors red, white, and blue were not considered in the initial adoption of the flag. However, as America congealed into a single nation, the colors began to take on increasing significance.
The thirteen red and white stripes that form the background of the flag contain multiple levels of symbolism. According to Charles Thomson, secretary of the Continental Congress, "White signifies purity and innocence, Red, hardiness & valour . . ."
The number of stripes is also historically significant. The thirteen stripes, along with the original thirteen stars, represented the number of British colonies that declared independence from England in 1776.