Civilization III didn't come with a built-in cheat mode, unlike Civilization II. Firaxis also hasn't released any official cheat codes for Civ3. The only known cheats are those tricks that exploit some bugs in the game and player-created cheat programs such as trainers and saved game editors. Some tricks that existed in the original Civ 3 were removed in the Conquests edition.
Here are some tricks:
(1) Trade for lots of money
Trade other civilization(s) for a map, some technology or a resource. Then ask them for 2 {with as many 0's you can fit} gold per turn. Stangely, they will accept.
(2) Efficient Trading
When another tribe asks you to trade, propose a counter offer. Once the counter offer screen comes up, click the items they are offering so that the 'What will you give me for this' option comes up, then click that. Now they will offer a list of things that (very often) weren't there in the initial trade, making your haggling profitable.
(3) Trade for everything
If you are at war with another nation, to trade for everything they have, type in as many 9s as you can in the money received per turn. They will willingly trade anything they have for one of your territory maps (or anything else).
(4) Edit mode:
Open the "civ3mod" file. This will open the game's editor, enabling you to edit units, technologies, civilizations unique powers, their stances, rare resources' show up , time of usage, effects on tiles, and much more.
(5) War Profiteering
Declare war on a defeatable civilization. When it is time to sign a peace treaty, add all of the enemy's cities available for acquisition (except the enemy capital), with as many 9's you can fit in the gold per turn box. After you get money, declare war again on that same enemy, then immediately ask for a peace treaty so you can keep the money.
(6) 36000 Points in 1 Minute
You can increase your score to 36,000 without building anything by creating a scenario with only mountains, where settlers cannot build cities anywhere. Play it on Deity level with as many computer opponents as you like. Since you can't build a city anywhere, skip your turn. The AI's will realize that they, too, cannot build cities and commit suicide in frustration. All enemy settlers will disband themselves on their first turns and you will score 36,000 points!
(7) Unlimited Gold
Unlimited Gold
This may only work in versions 1.29f and earlier. First make a backup copy of the file script.slc, which is located in:
..\ctp_data\default\gamedata
Then open up the original with any text editor and add the following lines:
trigger 'DOR_T_Give_Gold' when (IsHumanPlayer(g.player) && (player.1.gold<=200000))
{
AddGold(g.player,1000000);
}
(9) Reveal entire map and resources
Start a new game and enter "LeEmUr" as a leader name.
Save the game. Include the word "multi" in the saved game name. Load the game you just saved. You now can now see the entire map and all resources, begin with 100,000 gold, and be able to edit some game features..