The Creative Assembly is working on another expansion for Total War: Attila. The new campaign pack is called The Age of Charlemagne and is set during the Middle Ages.
This is how the press release describes the content:
In the largest Total War: Attila expansion to date, a brand new campaign map resplendent in medieval-style artwork focusses on Europe from the year 768AD. With the introduction of Knights, Housecarls and other new era units, battlefield conflict takes an iconic turn. With over 50 conquerable provinces and new campaign mechanics, a detailed and vibrant geopolitical starting position will offer hundreds of hours of gameplay."
Age of Charlemagne will be released for Total War: Attila on December 10. Here are some screenshots and the first trailer: