Military units lose 30 points per turn when on opponent territory.

I trying to figure out why my military units lose 30 points per turn, without beeing attacked, when on territory of a civilisation(Gajah Mada, Indonesia) I'm at war. I know it must be something like a doctrine, a wonder or religion or ... I hope this is not a permanent effect, because the game I'm playing is going so well so far. If you know what it is?

Emperor level

Your units are standing next to an enemy citadel. Either move away or have one of your units pillage the citadel.

Got it, thx very much Browd. I can now go back to serious stuff. Who knows, it might end up in hall of fames.
See you fellow fans!