Celtic Hordes is a mod for Barbarian Invasion which allows the Celts to form a horde. The idea came from a post on TWH, where someone said that the Celts should be able to form a horde. From there on, the mod quickly took shape, and was released soon after. I mainly did it to take a quick break from Britannia BC, which I then ended up doing hardly any work on for ages.
In the future, I intend to add more units to the Celts, both horde and non-horde. For example currently I have added Ireland as an AoR, to try making one before I need to make them in Britannia BC. Basically, this mod is what I will use to try things out that I may end up including in Britannia BC, to make sure that I can get them to work, and to learn how to do certain things, like make the damned campaign map work.