Silver ornament representing Thor’s hammer, dating probably to the X-XI century, discovered under fortuitous circumstances in the XIX century in Sweden, and subsequently given to the National History Museum (Historiska Museet), Stockholm.
The Mjöllnir hammer was the primary Thor’s attribute, the instrument provoking thunder and throwing lightning, which could kill but also bring the fertilizing rain. The beneficial function as fertility bringer of this weapon, which could assume also a phallic significance, is evidenced by the fact that it was put on the lap of the bride to consecrate a wedding union. Since Thor was at the same time a god of destruction and war and a deity who protected the dead, to whom were dedicated the inscriptions on steles, his hammer assumed the meaning of an object which could exercise its power over both life and death. In the narration of the killing of one of his goat, for cooking it, Thor brought to life again the animal through his hammer’s power. As a symbol of the fight of the god against the giants, it guaranteed the order of the cosmos, continuously threatened by the forces of disorder. In iconography, it is frequently represented in the shape of a cross, so much so that, during the conflict between the pagan religion and Christianity, it became the symbol which was opposed, and, at the same time, was regarded having the same value than the Christian cross. The obstinacy with which the Christians opposed the figure of Thor was in fact due to the permanence of his cult – mainly in popular religion – that more than anyone else strenuously resisted the introduction of the new religion.

[Source: http://commons.wikimedia.org/wiki/File:Torshammare_fr_Sk%C3%A5ne_ %28KVHoA_Akademiens_M%C3%A5nadsblad_1895_s102_fig82%29_vit_bakgr.jpg]