Lost Cities Wiki

This is an in-depth guide to building custom cities with Lost Cities, a Minecraft world-generation mod that produces ruined, overgrown cities. It has Forge releases up to 7.5.x and NeoForge releases from 8.0 onward.

This is not the official wiki

The mod's own documentation is at mcjty.eu/docs/mods/lost-cities. Read it as well. This site covers what that documentation does not: why a setting appears to do nothing, why a key copied from an example does not work in your own file, and how any of this reaches a world in the first place.

Who this is for

Anyone building a custom city for their own modpack or server. You do not need Java.

Before you start, you need to know:

• How a datapack is laid out, that is a data/<namespace>/... folder inside a world's datapacks folder or inside a mod
• How to find the config folder of your Minecraft instance
• How to read and write JSON by hand

Scope

Pages are written against Lost Cities 7.4.12 for Minecraft 1.20.1 on Forge, and most claims were read out of that version's own code and shipped content. A growing number have also been run in a world, and those are listed on Claim Tests. code review

The claim-test pack written for 7.4.12 also passes unchanged on 7.5.1, so the two share the same datapack behaviour even though 7.5 changed where cities put things. game test

The NeoForge line is no longer inferred. Every version below has been booted on the test rig and had its blocks read back out of the world, so a version-specific statement here rests on a run rather than on a key set. game test

Target	State
7.4.12, Minecraft 1.20.1, Forge	Primary. Every page here is written against it, and every claim pack was authored on it. game test
7.5.1, Minecraft 1.20.1, Forge	Runs the same packs unchanged, with one documented difference in how a building's palette is resolved. game test
8.2.2, Minecraft 1.21, NeoForge	Run in a world. A higher number than 7.5 and a smaller feature set, because it is pre-7.5 code ported forward. game test
8.4.1, Minecraft 1.21, NeoForge	Run in a world. This is where the 7.5 changes reached the 1.21 line. game test
9.5.1 and 10.0.1, Minecraft 1.21.11 and 26.1.2, NeoForge	Run in a world, all four packs, identical counts to Forge. game test
6.2.2, Minecraft 1.19	Run in a world. Builds a floor taller than 7.4.12 from the same file, because it has no overrideFloors. game test
5.3.29 and 6.0.3, Minecraft 1.18 and 1.19	Run in a world, and neither can place a predefined city at all. Datapack content still loads. game test
2.0.22 and earlier	A different asset system entirely, run on its own rig and covered in The File-Asset Era. game test

The Versions section covers the mod's history from Minecraft 1.11.2 to Minecraft 26.1, which asset system each release uses, and which pages here apply to it. code review

How claims are checked

Every claim on this site carries a chip saying how it was checked, and the chip is a link to the evidence in the claim register.

Chip	Means
game test	Run on a headless Forge server against a named pack, with the blocks read back out of the world. The strongest evidence here
code review	Read out of the compiled jar of the named version, with the class and method named
unverified	Neither. Not a synonym for false, and not a synonym for unknown: it is a statement about the evidence

A claim may be both game tested and code reviewed. It may not be unverified and anything else at once. The mod's own documentation and the official wiki count as neither, which is why several pages here disagree with them.

docs/examples/check_claims.py enforces it on every build: a block with no chip fails, a chip pointing at a register entry that does not exist fails, and a claim cited as unverified on one page and verified on another fails.

Two rules follow from that, and this site is written to both:

• A claim checked on one version is not restated as true of all versions.
• The mod's own code is the authority on what happens, and the mod's documentation is the authority on what is intended and supported. Where a config comment and the code disagree, this site documents the code and says so.

On 7.5.0 or later, read the 7.5 page before anything else

Version 7.5.0 added a planned road system and an inter-city highway network, and both are on by default. A setup that worked on 7.4.12 generates different cities after the upgrade, with no change to your config.

The clearest symptom: the mod refuses a building in any chunk the road planner has claimed, and it does so before it rolls buildingchance. Setting buildingchance to 1.0 no longer fills every eligible chunk. code review

What changed in 7.5 documents this, verified against the 7.5.1 jar. The same system is in 8.4.1, 9.5.1 and 10.0.1, unchanged. code review

Not sure which version you have? See Which version do I have.

The mod's own documentation

Read it alongside this site. There are three places, and they are not the same:

Source	What it is
mcjty.eu/docs/mods/lost-cities	The general mod documentation.
mcjty.eu asset-datapack page	The deeper page on the datapack asset system.
docs/asset_structure.md on GitHub	A newer and much longer reference covering the datapack assets key by key.

Those are the authoritative sources. This site adds depth on top of them and shows its working: each behaviour claim names the version it was checked against, and most were read out of the mod's own code or run in a world.

Where to start

You want to	Go to
Understand how any of this reaches a world	How It All Connects
Get your own building generating today	Your First Custom City
Look up a key	Reference
Fix an error you are looking at	Error Messages
Work out why nothing happens at all	When nothing happens

If you are new to the mod, read How It All Connects first, then follow the tutorial. The rest of this wiki assumes you know how a dimension reaches a world style.

Examples holds complete working files for everything the tutorial builds, and a validator that checks a datapack against the rules documented here.