Sega and Creative Assembly have released the Total War: Attila Assembly Kit–mod tools for the game. And no, you don't have to pay for them. Keeping in with the spirit of modding, the mod tools are free, as will all of the mods developed for the game through use of the tools.
While still in beta, the Attila Assembly Kit stands as one of the series' most powerful toolsets to date. Here's what comes with the toolset: Terry (Allows the editing of campaign map aesthetics), TeD (Creation of individual battle tiles), BOB (for processing data including textures, models, animations, etc.) and DaVE (the game database editor). They're each named after dudes.
In addition to all of the tools, there's the extensive Terrain Raw Data resource pack that includes 60 gigabytes of in-game production data for modders to check out.
For further details on the toolkit, check out the Total War Wiki.
