Well, maybe protect the head....? ^^ And the noze, the neck and the ears ^^?
No, seriously you have to take in account:
- its date (time of production and utilisation) and
- if this is an helmet for fight or if it is pageantry helmet, or even
- a 'simple' diplomatic gift (example with helmets offered to russian emperor) etc.. in this case it would be more jewerly than war practice object.
Anyway, the first aim of any helmet is to protect the head ( joke apart). This one I am trying to make/model/etc, looks pretty 'simple' but as it is a wip, you don' t see its chain mail all around it (hangs all around the helmet, on the ears, the neck, the forehead, and maybe the eyes).
In my humble & noob opinion in this matter, I would think that one of the most important aim of this helmet is to protect against arrows, and direct hit from hand weapon (contact fight, sword, hax, etc In this times, Islamic amrys was confronted to massive armys too, with massive number of archers, I guess. My personal opinion is inb its time and for what it was supposed to be made, it was maybe the best armors in the world at this time, relative to others armys ('ennemys') had at this time).
ps: this is a wip, this is not finished and have to be corrected in terms of scale, I' m speaking about the vertical protection for the noze, wich is larger and stronger, the decoratices pieces have to be corrected too in term of scale etc