From Osprey's publicity:
The Dark Age of Britain, from the middle of the 4th century to the end of the 8th, was a time of violence and warfare, when charismatic warlords such as the fabled King Arthur could gather together armies and carve out their own kingdoms. With this new set of wargames rules, players can take on the role of these warlords and command their own armies on the tabletop. Written by the author of the popular Glutter of Ravens rules set, Dux Bellorum is an element-based system, where each base of figures represents 50 fighting men. Each player has a specific number of points with which to construct his force and can choose to a Late Roman, Romano-British, Welsh, Saxon, Pictish, Irish, or Sea Raider army. The game is then played out following a set of simple, fast-paced rules. A completely self-contained gaming system, Dux Bellorum is perfect for gamers who are looking for a way into fighting Dark Age battles without investing a lot of time or money in larger rulesets.
From the playtest introduction:
Dux Bellorum is an Arthurian-era Dark Ages wargame, set in the period from the mid fourth century AD to the end of the eighth century AD. The rules emphasise the influence an army’s commander has on his units, with simple manoeuvre rules and chaotic, swirling close combat. You'll win by inspiring the right troops at the right time, balancing quality versus quantity in your army, and by finding a sprinkling of luck at the right time.
All distances are given in Base Widths, which allows the game to be used with any scale of miniature based in many different ways. An army usually has 6-12 units, and each unit is rated for Aggression (Attacks), Protection (Defence), and Cohesion (Strength) and is trained either as Shieldwall, Warriors, Riders, or Skirmishers (all of which operate differently in the game).
Dux Bellorum armies are selected from following lists: Late Roman, Romano-British, Welsh, Saxon, Pictish, Irish, Land Raider, Sea Raider.