HAHA I knew it! I wasn't crazy after all!
http://www.civfanatics.com/civ3/improvements/
Coastal Fortress
Cost: 40
Culture: 0
Upkeep: 0
Provides a naval bombardment defense of 8, +50% against naval attacks, and automatically bombards passing enemy ships
Building a coastal fortress shouldn't require a great admiral. Would be ridiculous. Although that would only be a sensible suggestion towards people that play only on tiny maps. That's just plain horrid idea for huge maps when there is easily hundreds of coastal cities.
If it really must be it, then it needs to be a deathstar of coastal fortresses, with normal coastal fortresses being built by workers or cities. Like how workers can build forts but only great generals can build citadels.