Start with a basic stone age palisade, then work up to a mediaeval Bailey followed by a keep.

Then, a more modern fort and battlements.

1)SAM sites & flak towers-air defense
2)Field hospitals-heal infantry units
3)Repair Bays-repair vehicle units such as tanks
4)Upgrade Center-upgrading obsolete units in the field
5)Trenchs-defensive bonus & units on them would be hidden
6)Military Labs-these specialized labs would contribute to research if the civ is reseaching military techs
7)Naval bases-placed on beach tiles, repair & upgrade naval unit
8)Improve the function of air bases to include repairing & upgrading aircrafts

civ III should keep other military tiles from SMAC & CTP II like bunkers & listening posts

Considering forts, like in CTP II, should be able to hold claims on land & different types should be available like Matthew said

1 other thing if there r like 4 or 5 different military improvments on 1 tile, the improvements should combine into 1 massive military base that offers all the bonus of all military tiles & maybe more

there should be future techs that give automatic defense tiles meaning that there doesn't have to a unit in that tile in order to defend against the enemy

1 last thing, Brent what do u mean by including walls, if there anyone who could explain it please do cuz i thinkin' u build the great wall of china & find it useless like in history

Ancient plow farmland: this is vastly good for dry plains especially on rivers, but doesn't work too well on wet plains where you end up getting to much water on the seed and having half the crop rot in the ground.

Mouldboard Plow Farms: These opened up europes interior to civilization later in history, it's heavier iron age construction and use of animal labor made heavy furrows in the wet plain, allowing for the successful planting of crops. A crucial invention as we get away from the mediteranean ocean and river valley civilizations.

Rice Paddy irrigation: This was china's solution to the wet plains problem, allowing them to slowly spread their civilization into new areas, and transforming their culture over time. Rice paddy irrigation started only on the rivers, and spread from their along CANALS, which took a lot of work to build and maintain, but produced MORE food then either kind of farming resulting in highly dense populations wherever rice could be grown.

Chimampas: The olmecs and later mesoamerican cultures didn't have to deal with wet plains, they had to deal with SWAMP and JUNGLE, the solution they came up with took as much work as rice paddies, and yeilded similiar results. The chimampas or floating gardens of the aztecs were able to produce three crops a year using the fertile soil dredged up from the bottom of their wetlands.

Gravel Pits: Gravel pits are a way of mining the plains, forests, and grasslands of the world, they come about later in history when larger amounts of dirt can be moved to make really big holes in the ground, but still don't produce quite as much as a mine would.

Orchards & vinyards - orchards appear later in the game when there is a degree of cultural stablility and a rich middle or upper class able to invest in long term propositions. These two advances turn hills and forest squares into tiles that produce LUXURIES and a small amount of FOOD, at the cost of production.

Canals: Canals are a great substitute for roads in climates where the weather doesn't get too cold and water is readilly available, they take more effort to build and maintain but also can allow for rice paddy cultivation, irrigation, and/or fishing, not to mention the INCOME generated by ease of travel, boats provide more trade then roads before the invention of cars, not to mention faster travel.

Some new tile improvements:

1. SAM sites, which would automatically bombard nearby enemy planes
2. Guard Tower/Ballista Tower/Cannon Battery/Machine gun post
3. Trech/Bunker
4. Land Mines, Sea Mines (hostile to all civs)
5. Missile silo (which can launch missiles, automatically and a specified target, if configured)

As for PW/Engineers, I think that farms, mines roads should be built by PW while SAMs, Towers, listening posts, airfields should be built by engineers

1)Deep mines. These would start like any other other mine, but on the discovery of a relevant tech (e.g metuallgy), a unit with the mining ability (either settlers or a devoted unit) could enter the mine and choose to construct a deep mine. From here the unit could act deep under ground and construct mining tunnels in every tile surrounding the original surface mine. The extra minerals produced would then appear in the tile of the original mine. Other techs could allow for the mined areas to be increased (up to 3 squares?) eg electicity, to power the pumps for air and water into the mine.

Each tile of tunnels would have a lifespan of 150 -200 years (about right I think for mines of this sort). The tile above these mines would also have the chance of being spoiled due to tunnel collape, evnironmental poisoning etc.

Once a mine has be exhuasted it could then be used for other purposeses, such as a heavy bunker or missle store.

2)Fishing Vessels. Once these are built they can be sent to a fishing ground (possible sea tile improvement). Here they would stay until they have collected a quoter of fish and then return to their home port and land the catch, adding it the to city store of food, then return to the fishing ground and so on.

The vessels would evolve over time from the small one man vessels to today commerical outfits. They should also be a target for enemy vessels.

now what i really would like in Civ 3, are specialized tile imporvements meaning they can only be built by a certain government

1)Manors-built by monachy & Feudalism government, the tiles produce more food & trade than farms, they produce even more if serfdom is enacted & less after serfdom is appealed

2)Villas-built by monarchy & feudalism government, the tile produces less food & trade than manors but a little more than farms, they provide defense bonus & units on the villas have reduced maintaince

3)Collective Farms-built by socialist governments, produce more food but less trade than farms & advanced farms

4)Shrins, temples, basilicas, cathedrals-built by theocracy & fundamentalistism(i think i spelled it right), produce more trade & increase happiness

5)Cybernetic Computer Nano-Centre-built by Technocracy & Virtual Democracy, boost science & trade

if you change governments, the specialized tile improvements would be still there but they lose their effect slowly & decay slowly to the point they disappear

Suburbs, these tile improvements are built next to metropolises, these tiles have increased tile production of all resources, if the suburb is built over a farm it produces more food. suburbs are random meaning you can't select to build them, they just build them self

Zoning tiles, this would set a tile to have one type of resource producing improvements, meaning you could build only one set of tile improvements. the zone tile also could increase in that certain resource, when your citizens start to developing them, this would make your citizens useful

could use feedbacks