Sci-fi virtual world EVE Online is getting a big new addition — really big. As part of its new "Citadel" expansion, which launched last week, the massively multiplayer game has added a new class of structure called citadels. They look like space stations, but they're so big that developer CCP Games describes them as cities in space.

"These monuments to the might and power of capsuleers make excellent player-run trade hubs and defensive platforms," the developer says, "the largest of which is massive enough to offer super-capital ship docking bays."

The citadels come in three different varieties — medium, large, and XL — and on the high end they're big enough to house some of the biggest ships in the game. Like most things in EVE, you can't just buy a citadel, but instead players will need to pool together resources and money in order to create one. But their sheer size means that they have the potential to turn the tide in EVE's famously complex universe, where player-run corporations vie for territory and power.

CCP says that a citadel can cost anywhere from 700 million ISK (EVE's in-game currency) to 120 billion. "A trivial price for a fortified city among the stars," the developer says. Citadels can also be destroyed, which should lead to some interesting power struggles for future EVE wars.