Actually, it could be lapis lazuli, that has been mined in Afghanistan for 7000 years now, and been of interest quite far from Afghanistan for nearly that long. The purple stone *could* be true porphyry, which was mined in Mons Porphyrtes in Egypt. If either of these IDs are true, this is not just another high-status Roman dwelling.
I looked up the lapis that certainly looks like it. the article does say it’s an Imperial Villa so you are probably correct. No expense was spared. Thanks!