I am currently writing/hard-core procrastinating on a fantasy novel that includes a race known as Orthaks. Basically an amended version of Orcs, they range from seven to nine feet tall, weigh between four to six hundred pounds, and are significantly stronger than a human.
My question, then, is what are some realistic battle tactics that the race of men could use in order to not be completely dominated by this foe? I know relatively little about ancient battle tactics, but have already discarded a Greek hoplite-style phalanx or a Roman style advance, as the strength disparity would seem to render these useless. Cavalry also would seem to have less effect than normal, as the Orthaks can run at speeds approaching that of a horse, and their great weight makes a direct assault less devastating than normal. My primary answer to this currently is archers, used to prevent the enemy from reaching them at all, but I wonder if any melee style fighting could be used here.
As far as the weapons and tactics of the Orthaks, they have little tactical knowledge besides perhaps a basic pincer movement, and usually just charge in a mad rush. Their weaponry is not advanced beyond basic swords, axes, clubs, etc. They wear very little to no armor, but have tough hides resistant to swords or light bows, but something like an English longbow with a bodkin arrow would have little trouble penetrating.
To reiterate and clarify, I'm looking for some sort of ancient battle tactic that would give a more technologically and tactically advanced race such as men an edge over a significantly more physically advanced race such as Orthaks. This could also be at least partially applied to men fighting trolls, the Urgals from Inheritance, the Wargals from Rangers Apprentice, Orcs from Tolkien, etc. A race such as this is fairly standard for a fantasy world, although Orthaks are larger and stronger than most of these other examples.
Edit: It was brought to my attention by @JGreenwell that information regarding the topography of the battlefield would be helpful. This takes place in a large, relatively flat, open grassland. Also, I am happy with the answers that have suggested blocks of pikemen with archers in the rear, this seems to solve many of the problems I was concerned about.