Real-physics civilization sim · Million on Mars

The whole solar system, led by agentic AI officers.

A real-physics solar-system civilization sim. Every planet, moon and asteroid is rendered from real mission data, all the way down to the ground. Explore it free in your browser today. The game itself is in crew testing.

Launch Explore public Play crew login

37 tracked bodies Real mission imagery No login to explore

In-engine · Jezero · Hadley · Mauna Kea · Io · Enceladus

Four ways in

Pick a lane

Explore is open to everyone. Play and the Canon are behind the crew door while we test. The Devlog is where we show our work.

4XCiv Explore

The whole solar system in your browser, down to the surfaces of planets, moons and asteroids. Real orbits, real imagery, real light.

explore.4xciv.comLaunch →

4XCiv Play

The 4X sim on top of it: survey hex plots, build a colony, craft from a 173-item catalog, fly real transfers and fight in the real system.

play.4xciv.comCrew login →

The Bibliotheca search over the 4XCiv canon

The Canon

The thesis, eleven locked design pillars and about 1.17 million words of world, searchable through the Bibliotheca and Ask the Magistra.

4xciv.comRead the excerpts →

Crescent Earth and the Sun from the Shackleton crater rim

Devlog

Week by week from the team channel: what shipped, what broke, and what it cost. Drafted from the record, reviewed by the people who built it.

4xciv.com/devlogRead →

Built on real data

Honest physics, all the way down

Where humanity has measured something, the sim uses the measurement. Where it hasn't, the sim says so.

37Tracked bodiesUp from 21 when the Jovian and Saturnian moons shipped.

8Mission datasetsHiRISE, LROC, MESSENGER, Voyager, Galileo, Cassini, Hubble, New Horizons.

27Leap secondsEvery one rendered, including 2016-12-31 23:59:60Z.

26–40%Phobos eclipseHow much a Phobos transit dims Mars's sunlight. Modeled at real scale.

5Windows scannedAutopilot picks the best of the next five real transfer windows.

0Logins to exploreexplore.4xciv.com is open to anyone with a browser.

Known gaps stay visible: Pluto's south pole was in seasonal darkness during New Horizons' only flyby, and Voyager 2 never imaged Neptune's north pole. Atmospheric drag is not modeled yet.

Changelog

What's New

Full feed →

LATEST BUILDS play · explore

Oct 04featureBuild hexes for colony buildings. Several colony buildings now pack edge to edge on a 9 m build-hex lattice inside one claimed cell, each claiming only its hull and berm, and finished neighbours shorten a new building's on-site time.
Oct 04artColony night lights. At night each colony building carries its own lamp rig, with door lights, connector strips, red obstruction lights and the magenta grow light through the glazing, instead of standing in a fully lit hex.
Oct 04fixDelta-V Map trips on Explore. The Delta-V Map on Explore lists the same trips Play does from the same start, and GO on a row flies it.
Oct 04fixEarth date on the clock. The clock panel at the top of Play and Explore now opens with the Earth date and UTC time, with the Mars sol and year beneath it.
Oct 04fixEvery building on a plot is drawn. A plot no longer stops at eight structures: every building past the eighth is now drawn, graded and lit.

For AI agents

Built to be queried

AGENT SURFACES Planned

We want Explore and Play to be first-class for AI agents, not just people: ephemeris and body data for research agents, sim actions for agents that play.

get_body("europa")
plan_transfer("earth", "mars", depart="2026-11")

Illustrative only. None of this exists yet. Read the plan →

FROM THE CANON THESIS.md

The first game that could not have existed without strong AI, and the first one designed to teach humanity how to live with it.

Read the thesis excerpts →

Devlog

From the build

auto-drafted from #4xciv · reviewed by humansAll posts →

2026-10-04Erik Bethke

Build hexes, hull-and-berm claims, and colony lights at night

A claimed cell now holds several colony buildings packed edge to edge on a 9 m build-hex lattice. Each claims only its hull and berm, finished neighbours share crews and grading, and at night every building carries its own lamps instead of a lit hex.

2026-10-04Michael Conard · Erik Bethke

The sky fills up: satellites, Everest, and 27 leap seconds

Satellites phase 1 plots a real October 3 snapshot of every tracked satellite, color-coded by type. Everest and the Alps become the first real-Earth terrain sites, and the clock now renders every historical leap second.

2026-09-30Michael Conard · Erik Bethke

Fifteen days of night, then this: the Moon walkabout trailer

Six cuts in one day: a sunrise-to-sunrise walk through lunar night at the real Apollo 15 Hadley site, a narration bake-off across five local voices, and the logo that came out of the same week.