Ecumenopolis

An Ecumenopolis represents the ultimate form of planetary development in Stellaris — covering the entire planet surface in continuous city, trading that transformation for a population capacity and output efficiency far beyond a standard world.

Prerequisites for conversion

You typically need to first convert your target planet to the matching base planet class, then progressively transform it into an Ecumenopolis through a dedicated planetary terraforming project. There’s also a second path: a Relic World specifically can be restored into an Ecumenopolis, which is otherwise one of the few terraforming options available for that world type. Either way, the whole process takes a while and usually requires a fairly high engineering tech level as a prerequisite.

Worth knowing going in: once a planet becomes an Ecumenopolis, it can’t be terraformed into anything else afterward — this is a one-way transformation, not something you can later reverse or redirect into a different world type.

Is it worth the investment?

Building or converting to an Ecumenopolis is expensive, but the long-term output efficiency gain is significant — especially valuable as your capital resource world in a tall build. If you’re going wide with resources already spread thin, it’s usually better to concentrate the conversion on 1–2 core worlds rather than spreading yourself even thinner trying to convert several at once.

Common question

Once a planet converts to an Ecumenopolis, its original natural environment and related output get overwritten by the city buildings — if the planet was previously an important resource source, weigh whether the conversion is actually worth it before committing.