Boris Gudenuf
Deity
Going to combine these two earlier posts, because they relate.1. With this. Should American Wildwest Forts counts amongs this as well as Spanish and Mexican Presidioes passed onto Americans? (And did US Army made use of any Presidios left over by Spanish and later Mexicans after 'Northern Mexico' changed hands in 1840s? (American-Mexican War, and later Gadsden Purchase with slightly more tracts of land transferred to the US controls in exchange of American dollars)
2. In Civ7. should Forts be a district rather than a TI? (which represents temporal stations)
I didn't know that forts don't exercise ZOC on cavalry. That's clearly an omission from Firaxis. If forts were able to claim territory (the tile they are built on and all surrounding) they would be awesome and I'd build them all the time.
The US Army 'forts' in the American west were scarcely fortified at all. The hoary old TV/movie image of a wooden palisade bristling with troops on walkways several meters off the ground was the exception, not the rule, unless the fort was being established in overtly hostile territory - like Fort Phil Kearney that was pushed right into Lakotah Heartland and guaranteed a hostile response. Most army posts were scattered buildings around a parade ground with no fortifications at all.
On the other hand, like the earlier European castles of 1000 CE and later, they did control the surrounding territory, acting as bases for cavalry and infantry patrols that made it nearly impossible for anyone with hostile intent to linger anywhere near them. And it didn't matter whether the potential opponent was mounted or not: even the very fast and mobile Plains Indians couldn't get away with stolen horses or other loot if chased by a Cavalry force, and raiding without getting away with anything was pretty pointless - something the Vikings had discovered 900 years earlier in northern Europe!
Forts also served to control territory from domestic disturbance as well as 'foreigners'. William of Normandy quickly built motte-and-bailey castles all over England after 1066, because they acted as fortified points from which to control the Saxon/English natives with relatively small Norman forces. He had, at that point, no real fear of foreign invasion of his new territory, all this construction was purely for domestic control. This was not that new: castles had been established earlier all over northern Europe both against the viking raids but also to control territory against domestic disturbances, which were far more common than was later admitted by the chronicles that concentrated on the nobility and their activities and not the disgruntled peasants and merchants.
So (at least in Civ VI terms), it would be appropriate for 'Fort' to be a District with a ZOC AND a 'Fort Bomb' mechanic to take control of the surrounding tiles.
BUT
Only if the Fort has a Garrison, without which it's just a bunch of buildings behind a wall/moat that anyone can walk into whenever they please. This was the problem with Pre-Conquest Anglo-Saxon fortified towns in the 8th and 9th centuries: the little kingdoms were too weak to provide garrisons, so in many cases the Vikings simply walked in and took control of the forts and towns for themselves (as you might guess from the examples, I just finished reading a recent history of the Anglo-Saxon kingdoms up to the Conquest, so it's all fresh in my mind!)
Here's where 'Forts' become Social/Civic Important. Frequently the Garrison was not provided by the State (or You, the Immortal Spirit of the Civ Omnipotent God-Emperor of Munificence, etc., etc.) but by local forces, like feudal warriors or a local town 'militia' not entirely under central control. Establishing these kinds of Local Forces leads to a more decentralized State automatically - and the kinds of internal problems brought on by having Cities and Nobles as powerful as the central government in the military force they have available, at least in their own part of the state's territory.
You want a strong central government and military, you have to find a way to pay for it, and whoever's paying will not be happy about that! (Cue the Roman Empire, Chinese Empires, - or 19th century USA, whose entire army in 1874 was less than 25,000 officers and men, half of them foreigners - recent immigrants from Europe)
Oh, and to be completely historically honest, Forts should require Maintenance to avoid them falling apart. Even stone walls weather, crack, crumble, and fires burn down the wooden hoardings (the upper walkways and firing positions) and the interior buildings. Any fortification left alone for long deteriorates sharply in its defensive capabilities, although it may retain some value as a Tourist Attraction (See Hadrian's Wall, England's fortified Manors, and the castles that litter Europe from the Danube to Wales and Scotland: Old Forts are a potential later Gold Mine)