Fixed map of Britain, could be set in the period 550 – 750, with preset factions: Jutes in the southeast, Saxons in the south, Angles in the north, Scots and Picts even further north, Britons in the west. The heptarchy, basically. Easy to make campaigns, wars and skirmishes between kingdoms/factions. Fighting off evil christian missionaries and the like.Roadnet could be modeled after existing roman roads (Fosse way, Watling street etc). Weaponry and armour a bit too modern for this period, but most people won’t care.
