The Long Sword made its first appearance during the 16th century. The sword was used for two purposes on the battle field. The first use was to break apart enemy pike formations. The sword would be swung to break the heads off the pikes, then used on the vulnerable pike men.
The second use for the Great Sword was as a defense against mounted charges. The long length of the blade allowed the sword to take out the legs of incoming horses.
This was the sword of the Knight during the High Middle Ages.