Just lazy, perhaps this has been beaten to death already but the coastall fortresses still seem at least partially like dead weight. Perhaps they do offer the passive defence and certainly seem to be the first improvement destroyed under naval bombardment but I still have never witnessed a costall fortress firing back at least not accurately enough to hurt the attacking vessel. Pisses me off especially since I am a lazy navy builder and hence tend to leve my coastall cities sitting ducks for enemy ships.
I'm trying to recall a vague reference from someone at Firaxis on this. The coastal fortress is mostly ineffective against modern ships. Against ancient vessels, it fires only when they move from one ZOC tile to another. Thus, they can sneak in and back out without being fired upon.
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"Entia non sunt multiplicanda praeter necessitatum." — William of Ockham