This is a typical
example of conical or "Norman" helmets. This bowl
shape seems to have proved an effective defence against swords,
axes and maces, since they remained popular in various part
of Europe, especially the east, until the thirteenth century.
This kind of helmet
could be made in two ways: the first one involved the welding
of two halves. A good example of this technique is the helmet
found in Orchowskie Lake, Poland. The second fabrication method
consists of forging the helmet out of one single piece of metal.
Such helmets would have been reserved to wealthy warriors. The
best example of this construction is the Wenceslas
helmet (available on this site).
(In part based
on : Arms and Armor of Medieval Knight by D. Edge and J. M.
Paddock.)