Quest for Glory 5 Dragon Fire

I'm badly stuck in the 2nd of the Rites of Rulership - "Conquest" - on the island of Sifnos.

I've killed all the guards (outside and inside the fortress) but now a Centaur Wizard has appeared in the fortress, upstairs on a walkway, and I don't seem able to damage him AT ALL

I'm playing as a plain and simple "Fighter" and have looked at a couple of walkthroughs for possible tips.
And the ONLY fighter tip I can find is to pick up some throwing spears (which I have done) and keep throwing them at the wizard until he dies.
However, as soon as I get near enough to aim one at him, my character is "auto turned round and runs a few steps away" all the time getting pelted by the wizard's magic, so of course the death of my character inevitably follows

Can anyone offer any help, please ??

Before going to Sifnos, buy about 50 daggers. When you get there, fire at will. The Centaur teleports, but with a thrown weapon, who cares? If you don't have the daggers, just snag spears off of that cart in the courtyard of the fortress - you can pull an unlimited number of them off of it

Minos has killed himself in his palace (and I've killed everyone else) and I've done the all important looting of bodies BUT I can't find a way to open the trapped gate of the "essential" alcove without dying.
As a Fighter I have no magic powers. [The only "magic" I have is that some of my armour is magic and I have one magic spear.]
But even with my health and stamina at the highest levels, I am instantly killed by the blast of the trap on the alcove door as it explodes.

Then pour fireproofing potion on yourself.

[/spoiler]I'm not sure I CAN disarm the trap because when I started the game I heeded the advice of "only developing skills in line with my character of a "fighter".
[Therefore no magic or thief etc abilities.]
So it looks like I will have to re-load a saved game from waaaaay back (before this recent lengthy period of combat where game saving is not allowed) and go buy myself some fireproofing. I reckon that could be a valid option
[I actually found that particular advice in more than one place after I started looking for help
Annoying because of course I could have bought some before setting off to the anticipated big fight - but I never thought of it !!!!]
Anyway, maybe with my health and vitality at full notch, fireproofing myself ALSO will be sufficient.
And I'll buy a few of the potions if I can because if I DO get past this part and have to face the Dragon I could well end up getting a trifle singed

However, all might have to wait a day or two as I can't spare too much time right now [spoiler]