[Stratos]

Well, a Monks AC is connected to his dexterity and wisdom scores and and those scores probably isn't anything you would put too much points in in a Fighter/Mage multiclass. The Monk has other benefits, though. A F/M is very possible but he'll be a worse figher than a pure-class Fighter and not that good of a Mage compared to a single class one. If you focused on one kind of weapon, ie. taking Weapon Focus and Weapon Specialization, plus used alot of buffing spells then you could have a good character. But magic and fighting doesn't really blend that well and there are no Prestige Classes, like the Bladesinger, available in any of the expansions to truly make a powerful F/M class.