This is a small mod that allows the Celts to form a horde in the BI campaign. It also adds a new province, in the area which is now known as Wales. The Celtic faction leader starts near to the settlement in this region, instead of in Tara, which is now rebel owned.
-First, make a copy of the contents of your BI folder.
-Paste this copy into your root BI folder, and rename the copy to celtic_hordes.
-Now, copy the contents of the .zip file into your root BI folder.
-When prompted whether you wish to overwrite any files, click Yes To All.
-When it has finished copying, make a copy of your RTW:BI shortcut on the desktop.
-Right-click it and click on properties.
-In the "Target" line, add the following onto the end of it: -mod:bi\celtic_hordes -nm
-click Apply and then OK.
-Double click this shortcut to run BI. The Celts will now be enabled in the campaign, and they will have the ability to form a horde when down to one settlement.