BRDs came about from Gridanian archers. The story goes that the Archers of Gridania are trained to observe everything in battle and never miss a thing as the role of the archer is to attack the right place at the right time to turn the flow of a battle. This also meant that the archers had to watch the slaughter of battle, the deaths and the tragedies unfold without ever looking away. Having seen so much, to cope with it some sought to express the pain of see all this through song. So some archers of Gridania began to sing in battle.

The generals discovered that these songs had a positive effect on their soldiers and a negative effect on their foes. They inspired bravery and resolve in allies and doubt in enemies. Several armies tried hiring professional minstrels to provide the support but discovered their songs didn't have the same effect. The reason was simple. A bard must understand the pain and loss. They must be able to empathise with the experience so their songs resonate with their souls. This is the heart of where the power of their songs come from. That's why the Archer and Bard are tied together.

That's roughly what I remember of the origins of the Bard. Moggles were thrown in their too a bit as Moggles understood the nature of the power of song and were great lovers of music.