Just a further note--the Spanish Conquistadors weren't the Roman legions. They were very different people with different ideas about combat. Even in the Romans' time, if you'd asked someone else how to fight you'd have gotten a different answer than you'd get from a Roman legionnaire.
When the Romans fought some of the Northern European tribes, for instance, they found that the "barbarians" used long straight swords which they swung, often round their heads, in long, powerful arcs designed to cut through an enemy entirely.
The "barbarians," to their dismay, found that to engage the Romans at close quarters they had to pack in tightly as the Romans did, and there was no room for their large, arcing cuts. The Romans, meanwhile, used short swords and stabbed from behind their tightly packed shields as they advanced. Great power in the thrust was not required for the Romans, because they could use their shields and their advance to "herd" and compact the enemy.
There's nothing very romantic or inspiring about the way the average Roman foot soldier fought, to my mind, unless it was the courage and strength of mind they displayed in not breaking their formations. Basically, he followed commands as closely as he could, stayed as close to his neighbors as he could, and stabbed whatever was moving in front of him until it fell down and he could stab the next one.