This bit of unholy prayer from a runestone in Sjonhem parish, Gotland. The carved memorial, which dates from the 11th century, is a memorial to Rodfos, son of Rodvisl and Rodälv, who died in southern Romania:

rąþuisl:auk:rąþalf:þau:litu:raisa:staina:æftir:sy[ni:sina:]þria:
þina:eftir:rąþfos:han:siku:blakumen:i:utfaru
kuþ:hiælbin:sial:rąþfoaR:kuþ:suiki:þa:aR:han:suiu

The interesting line here is the last one, which reads roughly: May God help Rodfos’ soul, and may God swike those who swoke him.

That peculiar verb, attested in Runic Swedish as svīk(v)a and classical Icelandic as svíkja, has a meaning of to betray, deceive, cheat, or defraud. (There are also some interesting attestations of compounds with the noun: svikadrykkr: poisoned drink; svikamaðr: traitor; svikdómr: treason.)

The OED gives the surviving meanings of the corresponding English verb to swike, which are admittedly obscure ‘except in Scottish dialect’: “To act deceitfully, to cheat, to ensnare,” and perhaps most interestingly: “to prove false to, to disappoint the expectation of.”

This last sense, I think, comes the closest to the emotion on the Sjonhem runestone: Radfos was swicken by “blakumen,” probably Romanians (lit. Walachians) who were out of the range of that familial revenge that would normally be meted out. Thus Rodfos’ family made a decidedly un-Christian appeal to a higher power in their search for vengeance.