The most common "Great Sword" was actually the Claymore, and if you know anything of history, there were no "large great swords." The Great Sword, as Witch has said, was used to fend of Pikeman, but was also used for horse back. The Claymore, and all other Great Swords, are actually built specifically for precision, that is why they are built so long, yet relatively light. They were designed to be a sword for slashing in large sweeps and piercing at a deadly close-inner medium range. On horseback they were used to stab their opponents from behind in the weaker folds of their armor and then they would swing the blade in slashing motions to stir the crowd and break-up a defense.