3Miro
Deity
Is this a bug, or a gameplay mechanic I've overlooked? The great Sea Walls of Constantiople kicking in?
What's the issue? Constantinople has the Theodosian Walls that provide huge defensive bonus. You can bombard that from the sea. This is standard BtS mechanics. Did you mean something else?
Plus, what's the deal with Hadrianople? No matter who holds the city (Byz, Bulgaria, Ottos), they often turn it into a massive citadel. Knowing this, I had to plan from the very beginning as Russia to beseige the city, building up a force of 40+ Boyars, 40+ pistoliers, 10 bombards, 10 musketmen, and 10 spies (to bring down the start fort and create revolts to stip city defenses) while building forces for my Lithuanian, Polish and Finno-Swedish campaigns. Fortunately I took Bulgaria, and they were kind enough to build Kalmar Castle for me, and Bulgaria, Rus' and Lithuania had settled several Great Generals in their key cities, so after settling my own GGs, I could produce several Combat 2 + Flanking 2 pistoliers (Flanking 2 is so awesome - 70% withdrawal chance CANNOT be underestimated & combined with combat = one badassed seige unit). I built several longbows in cities with ranges so I could upgrate to strong muskets to protect my Bulgarian cities, and then built muskets with Hillsmen 3 to fortify on the north Thracian hils to protect my cavalry stacks as they beseiged Edirne.
The other issue with AI turtling is lack of offense against a seige - with 40+ pistoliers in the city, the Ottos could have given me a true heartbreak by attacking my stacks with high withdrawal odds (since turn one invoved moving units to the hills outside town, and not being able to attack), but the AI never sends out more than 2 or 3 units from a turtled city like this (unless you occupy one of the 8 tiles bordering the city).
THe plan worked out for me, as I managed to bring down a city with 70+ units garrisoned inside within 3 turns, but it only worked because I knew this would happen - this one city always winds up a massive citadel. Is this behaviour something the AI is hard-coded to to, or is it just a quirk of the AI to garrison certian cities to ludicrous levels (I also see France/Burgundy/Dutch do this with Anvers/Antwerpen often, as well)? I probably shouldn't complain, though, as the alternative is seeing the military spread out to 10 + units per city instead of 50+ in one city.
I think the AI doesn't realize the withdrawal odds as in BtS one usually doesn't get +70% withdrawal. The general AI scheme of Civ 4 is very bad, every unit tries to figure out what to do by itself without consideration for other units. The concept of "guard my own territory by overwhelming the enemy with numbers" seems to be lost, all the AI sees is "the enemy is strong, I cannot win 1 on 1, so I'd better stay fortified in my cities".
The "every unit for itself" mechanics also leads to those huge stacks in the cities. Units try to find the best city to garrison themselves and it is always the same city. There is no general consideration about what other units are doing.
The worst example of this is when the AI has to use ships to transport units. This requires coordination of two units, which is next to impossible (when it happens it is purely by accident).
I will look into the unit AI mechanics, those haven't been updated in some time. There are XML flags telling the AI what different units could be used for.
I will see what I can do, but I don't hope for too much.