Well, after winning my first ever system from the hands of evil aliens (possibly precursors? I'm still not sure how to check if they are/were) I came across a planet with 101 ruined instillations on it. It had been guarded by two ships that I presume were PDCs, as they didn't move. So I brought up some xenoarchaeologists, as well as 4 engineer brigades. They started recovering instillations, but then something I hadn't expected happened: They discovered a Ruined City. This is apparently an event that stops the gametime from continuing, however I cannot for the life of me work out what's so special about it. It appears on the populations list in System view, but that's it.
tl;dr: What is a ruined city?
On a slightly unrelated note, do combat-dropships have to have a troop transport bay as well as the drop pods, or not?
Thanks!