They still don't happen! The conditions for the "Marians" are met now for 3 consecutive turns.

The following questions turn up in my mind:
- do they need Roma or an Italian settlement for the Marians?
- do they need the Polybian markers present in their currently held settlements? -Currently they do not own any settlement with the Polybian markers

Also, the requirements for the Casse invasion are met since ~40 years. Still no sign of an invasion. It could have happened three times by now.

I'm not that good at maths, but I just calculated the chance for not having the Marians after three turns with a 99% chance of getting them is 1:1,000,000.