C3X

C3X is a free fan mod of the Civilization 3 Conquests program (Civ3Conquests.exe) that fixes long-standing bugs, speeds up late-game turns, improves the AI, removes the unit limit and adds options for players and modders; it works with the Steam and GOG Complete, installs by running INSTALL.bat in the Conquests folder, and does not officially support online multiplayer.

10:34 C3X is a fan mod that changes the Civilization 3 Conquests program itself: its README on GitHub calls it "a mod that makes many improvements to the Civ 3 Conquests EXE", fixing long-standing bugs such as "the infamous submarine bug", speeding up turns, letting the AI use artillery and armies, removing the unit limit, and adding stack commands and a warning before cities riot. It works with the Steam and GOG versions of Civilization 3 Complete, leaves saves readable by the unmodded game, and changes no rules unless you turn an option on. Because it edits the program rather than the rules files, it reaches what the game's own editor cannot (see Editor and Modding).

Quick facts

What it changes	The Conquests program, Civ3Conquests.exe
Works with	Steam and GOG Complete; the DRM-free PCGames.de program for CD owners
Install	Copy its folder into the Conquests folder, run INSTALL.bat
Backup it makes	Civ3Conquests-Unmodded.exe
Settings	INI files: default, scenario and custom
Online multiplayer	"Not officially supported"
Limits	Unit limit removed, 256 improvement types limit removed, city limit raised to 2048
Code on GitHub since	Sep 10, 2021 (GitHub API)
Latest on GitHub	Release 27 Preview 2, Apr 26, 2026 (GitHub releases)
Home	CivFanatics, its "primary home"

Source: C3X README on GitHub, read Oct 22, 2026, except where linked.

What C3X fixes

C3X fixes long-standing bugs in the Conquests program, whose last official patch was v1.22 of Apr 5, 2004 (the official support page). The README lists the "submarine bug" (AI paths colliding with invisible units), the "houseboat bug" (a crash when an AI civilization survives with only a Settler on a transport), the "phantom resource bug" (resources beyond the first 32 sharing access records in cities off the main trade network), science age beakers that were never awarded, air units losing a turn after being set to intercept, and several crashes, among them cities with zero production.

It also makes late-game turns faster. The README says it fixes "a major inefficiency in the game's sea trade computation", which it calls "one major cause of slow turns in the late game, especially on large maps with many coastal cities and many wars".

What C3X adds for players

The best known addition is stack commands. Holding Ctrl turns most unit buttons into stack buttons that give the order to every unit of the same type on the tile, so all Workers on a square build a railroad at once and all bombers bombard together, the README explains. Ctrl also stacks fortify, upgrade and disband.

Other conveniences it lists:

A warning from the domestic advisor if you try to end the turn with unhappy cities.
Arrows on the trade screen to switch between civilizations, and gold amounts filled in with the best figure (the most the AI will give, or the least it will take).
Units grouped on the right-click menu ("3x Spearman"), with icons for movement and combat status.
Golden age turns remaining, tile coordinates, and detailed city production.
Research spending cut automatically to avoid bankruptcy.
An option to replay AI moves for every human player in hotseat games.
Fixes for graphical problems under Wine.

A smarter AI

C3X changes how the computer players fight. The README says the AI "can now use its artillery units in the field", taking them out of cities to bombard enemy cities and units, builds much more artillery to do so, and "can now use armies properly", building them and filling them with its strongest units (a bug had kept the AI from filling its armies). On how the base game's Great Leaders and Armies work, see their page.

A platform for modders

C3X lets modders change rules that the editor cannot. Every such change is off by default ("the rules are not changed from vanilla Conquests unless the config file is edited", the README says). Among its engine extensions:

Limited railroads, working as in Civilization 4 or as fast roads.
No trespassing without a Right of Passage, and a stack limit per tile for land, sea and air units.
Buildings that generate resources, and buildings required to build a unit.
Civilization and leader names that change by era.
An adjustable city work radius (1 to 7 tiles; 2 is the standard), and an adjustable minimum distance between cities.
Lethal zone of control and defensive bombard, and land units that can bombard ships in cities.
Adjustable Anarchy length, and corruption removable for a government.
"Districts", which it describes as "an elaborate change to the game's economy inspired by Civ 6", with its own CivFanatics thread.

It also re-implements the "no-raze" and "no unit limit" changes of earlier modified programs, removes the limit of 256 city improvement types, lifts the city limit to 2048, and removes the cap on the turn limit. It ships an AMB Editor for the game's .amb sound files.

How to install C3X

C3X installs by copying its folder next to the game and running a script. The README gives these steps:

Extract the mod into its own folder.
Copy that folder into your Conquests directory, the one that holds Civ3Conquests.exe.
Double-click INSTALL.bat. A message should report that the installation succeeded.

If the game is installed under Program Files, INSTALL.bat may need to run as administrator. The installer keeps a backup of the original program as "Civ3Conquests-Unmodded.exe"; to uninstall, delete the modded program and rename the backup to "Civ3Conquests.exe". The mod folder must stay, because the installed game still uses files in it, and a new version can be installed over an old one. RUN.bat starts a modded game without installing, though the README says it does not work for some people.

Settings

Every C3X feature is set in INI text files. The README names three, loaded in this order: "default.c3x_config.ini" in the mod folder, a "scenario.c3x_config.ini" in a scenario's folder for that scenario's rules, and "custom.c3x_config.ini" for your own preferences. It recommends putting personal changes in the custom file, since the default one is replaced with each release; for example, group_units_on_right_click_menu = false turns off the grouped right-click menu.

Compatibility

C3X runs on the editions sold today: the README says it "is compatible with the GOG and Steam versions of Civ 3 Complete" and with the DRM-free program from PCGames.de. Owners of the CD version can put that program in place of their own and install C3X on top. Saves made before the mod load with it, and saves made with it still load in the unmodded game.

Online play is the exception. The README says "Online multiplayer is not officially supported": some features work and others, such as stack commands, do not, and it has reports of crashes in online games. Hotseat play gets several options of its own, such as shared visibility for human players. See Multiplayer for how online play works on Steam.

For Macs, the README points to a CivFanatics thread on running Conquests on Apple Silicon; no Mac build of the game is sold. More on old Windows problems such as the disc's copy protection is on Running Civilization 3 Today.

How C3X works

C3X patches the program and injects new code into it. Some parts, the README explains, "are really just hex edits" to the program code (the bug fixes, no-raze and the unit limit); the rest is "a system to compile and inject arbitrary C code into the process", built on TCC (the Tiny C Compiler) and on Antal1987's earlier work mapping the program's internal structures. The README says "C3X is open source" and names its source files, though the repository has no license file (GitHub API).

Releases and where to get it

C3X is released on CivFanatics, which the README calls its "primary home", with its main mod page, release notes and discussion thread there. The GitHub repository, under the account maxpetul, holds the code and preview builds: its newest is "Release 27 Preview 2", published on Apr 26, 2026, and its code was last updated on Oct 13, 2026 (GitHub API). The README links a video by Suede, "C3X: Incredible Quality of Life mod for Civ 3", which shows how to install the mod and some of its features.

Frequently asked questions

What is C3X for Civ 3? C3X is a free fan mod of the Civilization 3 Conquests program that fixes bugs, speeds up late-game turns, improves the AI, removes the unit limit and adds stack commands and other options, per its GitHub README.

Does C3X work with the Steam version of Civ 3? Yes: the C3X README says it works with the Steam and GOG versions of Civilization 3 Complete, and CD owners can use the DRM-free PCGames.de program with it.

How do I install C3X? Copy the C3X folder into your Civilization 3 Conquests folder (the one with Civ3Conquests.exe) and double-click INSTALL.bat, which backs up the original program as Civ3Conquests-Unmodded.exe, as the README explains.

Does C3X remove the unit limit in Civ 3? Yes: C3X removes Civilization 3's unit limit, removes the limit of 256 city improvement types and lifts the city limit to 2048 (C3X README).

Does C3X work in multiplayer? Not officially: the C3X README says online multiplayer "is not officially supported", some features such as stack commands do not work there, and it can cause crashes; hotseat games have options of their own.

Can I uninstall C3X and keep my saves? Yes: delete the modded program and rename Civ3Conquests-Unmodded.exe back to Civ3Conquests.exe, and saves made with C3X still load in the plain Civilization 3 Conquests game (C3X README).

Where do I download C3X? C3X is released on CivFanatics, its "primary home", and its code and preview builds are on GitHub, where the newest is Release 27 Preview 2 of Apr 26, 2026.