Murmillos are an Imperial Medium Class gladiator which are encountered fairly often throughout the game. They have above-average Defense for a Medium class, but are mostly average in other attributes. Their Constitution tends to be a little bit lacking, possibly to balance out their Defense, and their speciality lies in dealing with Support Class gladiators. A murmillo named Priam is an antagonist who must be defeeated in one of the Imperia side-quests.
The Murmillo has a very impressive set of skills, with many powerful Attack moves and some nice Innate abilities. The Throw Shield line of Attack skills are the trademark of the Murmillo class, and are very powerful medium-range projectile attacks. The improvement in range and damage versus SP cost is most practical from Throw Shield 1 to Throw Shield 2, but it is still worth getting Throw Shield 3 for situations that may require it's additional area of effect.
Bull Rush is a guaranteed hit that will do considerable free damage to Light gladiators who are two or three spaces away from the Murmillo (it affects all Gladiators but is most useful against lightweights). Shield Ram only costs 1 SP and can knock down the opponent, allowing for free hits from your other teammates until the opponent can get back up again.
The Murmillo's Innate Skills are also very useful. Shield Mastery is not entirely necessary due to many of the Mumillo's better shields being unbreakable, as it only increases their durability. Advanced Block combined with Shield Counter, Humiliate and Off Balance makes for a devastating effect on anyone who misses the Murmillo, which will happen quite often. Arrow Guard will reduce the damage you take from projectiles and Incoming will aid your nearby teammates in avoiding projectiles.
The Murmillo is an invaluable addition to your school for battles against Support Classes such as Archers and Peltasts. Keep your Murmillo close to your other teammates for maximum effect from the Incoming skill, and make good use of your Throw Shield abilities to beat out the ranged attackers at their own game. Murmillos are also deadly effective against Light_Classes, since Light gladiators rely a lot on their Accuracy which the Murmillo can easily counter with their high Defense.
When fighting against Murmillos at higher levels, it can be quite intimidating to see a 5% chance to hit with almost any attack. Aim for critical hits or use a Samnite with guaranteed attacks such as Power Bulldoze. Surrounding the Murmillo at close quarters also works well since they generally do better at range or against a single opponent. Whatever you do, don't take on a Murmillo alone with a Support or Light gladiator, it's just never a good idea.