Tyr is the original skyfather in heathen mythology. His major sphere of influence is justice. Zisa is his wife. Her symbol is the war boat, and she was identified by Tacitus as being the same goddess as Isis.
The Fireverse uses the names of gods as recorded in the Icelandic / Norse sources, unless the name is not recorded there. In the Icelandic, the name of Tyr's wife is not written down. However, Tyr is the same god as Ziu, and Ziu's wife's name is Zisa, so in both my novel Some Say Fire and in my personal practice I call them Tyr and Zisa.
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The war-boat as a symbol of Isis who was worshipped by the Suebi is from Tacitus’s The Germania. The Ziu / Zisa connection is ling
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Zisa is not mentioned by Tacitus, in Germania Tacitus mentioned that 'some of the Suevi also sacrifice to Isis' , Tacitus does not