Terra

Terra is the capital of the Imperium and the birth-world of humanity, a hive world so built over that open ground is held only by the powerful. The Emperor sits on the Golden Throne beneath the Imperial Palace, while pilgrims, clerks, and soldiers crowd the streets that remain.

Terra was the ground of the Siege of Terra, which came at the close of the Horus Heresy, the civil war that split the Imperium. Sanguinius fell defending the walls of the Palace during that conflict, and both Russ and Magnus have walked its halls.

Terra remains the most heavily defended planet in the Imperium. It anchors the Sol System alongside Luna and Mars. After the fall of Cadia, Guilliman returned to Terra with Cawl, Celestine, and Trajann Valoris to reopen the Indomitus war.