what is the name of this font??

Omnia  Suggérée par Astrud 

Its name is Omnia

I'm not sure what it is, but it is not Omnia, as only some of the glyphs in Omnia match up to the typeface of the Amon Amarth logo. I will do some research and get back to you when I find out which font it really is.

Letters are in a style called Uncial. Sometimes also called Irish, Celtic, Gaelic, Lells, Gandalf etc.
Did not spot a matching font. Might be custom lettering.
You might find a somewhat similar substitute among the Celtic fonts hosted here at Dafont
http://www.dafont.com/theme.php?cat=403&fpp=100&text=AMON+AMARTH+amon+amarth