The Battle Day is a highlight of the Society of Ancients calendar, when we all gather in Bletchley to refight a historic battle with as many different rules-sets as possible, all in the same room.  Interspersed with a talk and Q&A session normally given by an expert in the battle under consideration, it is both great fun for the participants, and a great way to see how different rules compare, and what they each do well and not so well.