There are (at least) 2 different bands using this name:
a) Reflecting the dual culture of their home region in western Finland, Gjallarhorn use both Finnish and Swedish traditional music as the base for their unique vision. Surrounding Jenny Wilhelm’s gorgeous vocals are a diversity of sounds from other parts of the world, making this a truly global Nordic journey.
b) An Italian Epic Viking Metal band, whose lyrical themes mainly deal with those of Ragnarok. They have only released one album (“Nordheim” in 2005). Their style is somewhat reminiscent of Hammerheart-era Bathory, with slow epic songs performed with clean vocals.
2 members of Gjallarhorn also play in the Epic Viking/Doom Metal band, Doomsword (Deathmaster and Wrathlord).