Oh,

Thats because its proving to be an excellent buffer zone against the aggressive ai so helping in keeping my alliance with Zhe Germans.
Otherwise they would betray me in a split of a sec.
you know how vastly superior the ai’s diplomatic skills are compared to ours right?

Even the dacians are proving to be far less aggressive.
I use this tactic once or twice in almost every of my campaigns.
None seem to be very much interested in attacking senat settlements.
Don’t even think I ever seen it happen though I’m not sure