We've all probably scratched our heads at one point wondering why the AI would refuse to launch an obvious naval invasion on one front, and yet pour counterintuitive invasions on another. Its decision making is too hard to predict. Thus we often have to fortify ALL of our coastal regions with garrisons or navies. Even worse is that the AI maritime invasion routes seem to change every time a new version comes out. This is where this thread comes in: to document each "stranger" AI naval invasion route so we can fortify the right regions. Note that the following list is for when one of the settlements is owned by the player. The AI seems to abandon certain invasions (Taras <-> Epidamnos) when one of the settlements is owned by the player.

Here are the "obvious" ones that the AI completely ignores (remember this applies if the player owns one of the settlements):

Literally any West <-> East Aegean invasion route EXCEPT for Athenai <-> Rhodos
Italy <-> Greece
Italy <-> Sicily
Italy <-> Illyria
Literally any Black Sea naval invasion route

Here are the "counterintuitive" ones that the AI takes anyway:

Pergamon <-> Rhodos
Pergamon <-> Knossos
Knossos <-> Syrakousai
Histrie <-> Sinope
Knossos <-> Rhodos <-> Alexandreia <-> Salamis (the quad network of doom)

The overall theme is that the Italians will mind their own business provided you own the surrounding regions, and that the island of Krete is, as always, a PITA to maintain. So feel free to leave Italy or the regions across the sea minimally garrisoned, but keep an entire damn army stationed in Krete at all times.

Seems like AI naval behavior is tied to faction personalities in descr_strat, decision-making in descr_campaign_ai_db, and region pixels in any of the data/world/base files. What's especially important is how much movement armies and ships have: more movement means more single-turn decisions by the AI, which encourages single-turn naval invasions. This link may also help: https://www.twcenter.net/forums/show...-invasion-help