"When I went there for treaty affairs aboard the Poseidon, I didn't expect to look out the porthole and see super-cities each spanning over one hundred miles each dotting the little planet's surface."
―Petty Officer 2nd Class Ron Johnson, crewman of the UNSC Poseidon
En is a heavily urbanized moon and is the pride of the Jiralhanae's terraforming ablility. At one point, it was seen only as a barren moon with a small amount of oxygen in its atmosphere (approximately 12%). However, it would grow to be one of the largest known colonies of any species before the 2630's. This large population quadrupled when Doisac and other Jiralhanaean colonies were evacuated to En. It is also well known for its landscape; by 2580, 65% of the moon's surface had been converted into mile-high cities and was a prime source of various spacefaring craft for both the Covenant and commercial use.