The Icelandic Commonwealth, settled disproportionately by small holders fleeing the growing impositions of the king and nobility, was a Zomian population many libertarians are familiar with. The Icelandic settlements recounted in the Sagas took place at a time when kings on the Scandinavian mainland “were enlarging their authority at the expense of the traditional rights of free farmers.”  King Harald Fairhair, for example, imposed taxes on previously allodial land, with the jarls under him keeping a share of the tax revenues for themselves.  The families who fled the continent consciously structured the new society along comparatively egalitarian lines to avoid such evils. 
According to Kropotkin, medieval towns—and the entire country of Switzerland, for that matter—were such areas, made up of runaway serfs and other populations attracted to territories with a prohibitive cost of governance. Paralleling the towns’ building of fortifications, federation and revolt against the authority of feudal lords, in many places villages federated together to resist their feudal lords. In most cases, lacking the protection of walls or defensible terrain, they were quickly defeated. But in favorable defensive terrain like the Alps, “such peasant republics became independent units of the Swiss Confederation.” 
40 Jesse Byock, Viking Age Iceland (Penguin, 2001), p. 65.
41 Ibid., p. 83.
42 Ibid., p. 84.
43 Pyotr Kropotkin, Mutual Aid: A Factor of Evolution (New York: Doubleday, Page & Company, 1909), pp. 206-207.