By using Protective Spirit and by equipping five Superior Runes and a unique Grim Cesta (obtain only as a reward for Cities of Ascalon quest), a Monk will only take a maximum of 5.5 damage (though the game seems to round the exact amount) per hit. Obtaining "Invincibility" can be done in a multitude of ways, the most popular being regeneration and/or by use of Shield of Absorption.