Other interesting facts from civ III included posts and airports. Posts were fort-like improvements that gave you visibility but consumed the worker that built the post. However, this protected the visible area from barbarian camp appearance. On the other hand, forts weren't able to carry air-units, only airports could.
Finally, the most interesting according to me was the respawning. If you conquered a civ, it could respawn again! I don't know what kind of system Firaxis used.
Moreover, instead of open-borders there was a double "right of passage agreement". It was possible to give a civ the right of passage without be given it back. However, you were able to move in any land without declaring war. It gets even worse. When a "right of passage" agreement was cancelled your units weren't expelled, so you could open border a rival, move your troops by his cities and capture him next turn.
You couldn't move your units in already occupied tiles. That's why AI prefer to defend their cities with units. It was a system to protect AIs from player abuse in civ3
You could cancel any agreement whenever you wanted. For example, you could trade a peace treaty and continue the war

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Overlaping city radiuses wasn't a problem. A common tile could be worked by either city.
Workers and settlers were trained exclusively by hammers. But, when a worker was finished the city lose one population. When a settler was finished the city losed two populations. Moreover, workers and settlers could join cities (add one population). When you captured foerign workers or settlers (which were converted to workers), the workers kept their nationality, even when they joined cities, and could be traded as "release my people" in peace treaty negociations.
In the industrial era, polution was created by unhealthiness and some tiles converted into unworkable from polution. It worked the same way "fallout" feature works. You should send your workers to srumb poluted tiles.
Oil resources were exhausted.
There was only one category of civics.
You could convert the production, and overflaws were lost...
Expansion was never penalised. On the contrary you should expand as much as possible if you wanted to survive...