The UK Battlefields Trust has an extremely interesting site with information, maps, ground and air photos of English battlefields from the Celtic and Roman periods through the Stuart uprisings.
Inspired by some shield designs and banners I recently saw from Little Big Man Studios (is this the first time a gamer has ben inspired by decals — it may be), I’ve been looking for information on Aurthurian Britain. The Brittania site has some terrific historical information on King Arthur.
Caliburn’s Wrath is a set of free wargames rules from Matt Cappetta for the Arthurian period. The rulesCaliburn’s Wrath are “intended to represent intense clashes between small bands of foot soldiers.”