First of all, it depends on your graphics card if it's possible at all and how to activate it. I can only tell how it's done with the DirectX 12 version on a Nvidia GeForce 970 (so with AMD cards the first part will be different). Unfortunately my system is in German, so the actual English phrasing might be a bit different.
- Open the
NVIDIA SYSTEM SETTINGS (for this the correct NVIDIA driver need to be installed of course)
3d settings go to
Surround, PhysX configuration
- Tick the check box under
Surround-Configuration that should state something like
Span over multiple displays with Surround and click on
- Select both monitors by ticking the check boxes. Check for the correct monitor alignment. Note the resolution (e.g. 3840 x 1080), and modify if needed. Click
Activate Surround function, and close the config window.
Now your Windows desktop should be spanned over both monitors!
Next we need to config Civilization VI itself.
- Go to
%USERPROFILE%\Documents\My Games\Sid Meier's Civilization VI\ (if using Windows 10)
RenderHeight to the configuration noted above (e.g. 3840 and 1080)
- Save the file
Now when you start the game it should run spanned over both monitors!