Which is just another one of those really odd, counter-intuitive things in PoE. Monk with a (non-fist) weapon? Monk with a shield? Monk with... heavy armour?
The RPG Monk was primaly based on the buddhist shaolin monks, so that's why we commonly portray them as warriors who fight barehanded and unprotected. The mere thought of monks employing weapons and heavy armor may sound alien, buy like salo already said, there is also a few monastic orders of armed monks in our history, like the Knights Templar, the Teutonic knight monks and the Sohei warriors of feudal Japan. I love the fact that the monk description in PoE embraces multiple creative origins other then "kung fu wacko".
Geralt from the Witcher series is a good example of fiction armed monk that could very well fit into the world of PoE.
Witchers are an elite caste of warrior-monks taken at a young age to an ancient fortress and experimented on to give them superhuman abilities. Those who survive the rigorous trials are extensively trained in a multitude of skills in preparation for defending Humans from beasts.
Geralt is a master of swordmanship, but he's also known as being extremely skilled in hand-to-hand combat, so that was probably part of his Witcher training. His fighting style transcends mere physical combat, and moves into the more intellectual domain that the Monks tend to dwell in. It's said in the books that he flows through his moves, almost as though he’s dancing. It’s a power that speaks of mastery of his art, as well as mastery of his own body.
TDLR Witchers could very well be armed monks in PoE. The only aspect that the Monk class doesn't cover is the minor spellcasting, but witchers should rely mostly on their weapons anyway so it's not a big deal.