The AI can also do exactly what bg9 asked about: Unsettle a GP and then use their one-off special ability. Also, bg9, you should know that the AI can "teleport" troops onto their ships at sea. So just because a galley has been hanging around doing nothing for a bunch of turns does NOT mean that an army of attacking units cannot suddenly unload from it! That for instance, a galley which entered your waters in the ~1000bc era can suddenly disgorge knights the turn after the AI civ gets Feudalism.
Hey, since I also made the jump straight from Civ2 to CivRev, I am going to presume to give you a little bit of more general advice. Because the maps in Civ2 were so much bigger than the maps in CivRev, Civ2 tended to reward a more passive program of research/expansion in the early game. In CivRev, it almost always pays to go on the offensive early in the game. A commonplace strategy among advanced players is to put both of your capital's workers on forests, produce 1 or 2 warriors to explore and then switch both workers to sea squares in order to research Horseback riding. As soon as you finish HBR, switch both workers back to production. If you have any money, rush the horses. If you have located an enemy cap, go right for it once you have a horse army. Two horse armies is usually the most I create. after about 2000bc some of the AIs will have archer armies and capturing their capitals is all but impossible with horses, so speed is crucial. My games pretty much boil down to this:
Get no capitals early=tough game
Get one cap early=easy game
get two caps early=the game is over, the AI just doesn't know it yet.
Only about 1 in 5 maps are the closest enemy AIs so far away that I cannot get horses there in time to conquer it.
I hope that is helpful.