It was Hiawatha ... who bound together the five arrows. One arrow alone, he said, can be broken, but the bundle of five is too strong. The structure of the Iroquois Confederacy became the model for the colonist's new union, and the symbolism stands today: the eagle in the great seal of the United States holds those five arrows  in its talons.
From The Rights of the Land by Robin Kimmerer in the November | December 2008 issue of Orion Magazine.
Kimmerer's piece, about a unique suit brought by the Onondaga Nation to regain legal responsibility for their ancestral lands surrounding Onondaga Lake, is unfortunately only available in the print edition.
Onondaga Lake is now a superfund site due to industrial misuse. The Indian nation has introduced a suite that "is unheard of in American property law":
The suite is termed a 'land rights action.' When they finally got their day in court last October, members of the Onondaga nation argued that the land title they're seeking is not for possession, not to exclude, but for the right to participate in the well-being of the land. Against the backdrop of Euro-American thinking, which treats land as a bundle of property rights, the Onondaga are asking for freedom to exercise their responsibility to the land.
 Thirteen, actually, for the thirteen colonies. It's the origin of the symbolism that's of interest in a country that rarely acknowledges its indigenous precedents.