This is an accompaniment to the Twelve Days scenario posted by Angrod.
For the full Twelve Days experience, please:
1. Copy the file "Pari Passu 12D.mp3" to the "Caesar IV\Data\Audio\Music\Main Game" folder.
2. Rename the existing file "Pari Passu.mp3" to something like "Pari Passu Original.mp3"
3. Rename "Pari Passu 12D.mp3" to "Pari Passu.mp3"
The Christmas medley should play something like once a game year. When playing other scenarios, you should reverse the above i.e. change the names back to "Pari Passu 12D.mp3" (or delete or move somewhere else) and "Pari Passu.mp3".
Note that this is entirely optional - you don't need this file to play the scenario.