Following up on my article on the mechanics behind Skirmish lists with an article on Division lists.
Division lists are both similar and different to Skirmish lists.
The similarity lies in how you construct each regiment, which is the building stone of your Division. Regiments are made up of several banners/companies/sotnia's or whatever units are called by each nation. And just like in Skirmish lists the Regiments are made up of a core level amount of troops, optional add-on units and additional troops that expand you regiment. Regiments also have their own Regimental commanders and junior officers to help you control the regiment in the field.
Check the blog for more detailed information on how Divisions in By Fire & Sword are put together:
http://anatolisgameroom.blogspot.se/2013/05/by-fire-sword-division-list.html