I learned a lot with this tutorial. Besides Shape3D, it is so neat how the mirror over line and tube oblique work.
I looked at pictures of helmets for inspiration, and a lot had the centre band. It took a while to figure out how to do it, and I couldn't explain it now to save my life.

I remembered the movie, and was thinking about using a picture from it. This one came up while I was searching.
In my quest, I also learned that the vikings did not wear horned helmets.

Those are from the Bronze Age, way before the Viking Age, but same part of the world. And they still look darn cool.
Moving on to my next tutorial - barbieq's jewel.