Côte d'Azur
From Halopedia, the Halo wiki
Côte d'Azur was the main population center of Sigma Octanus IV, a UNSC colony world in FLEETCOM Sector Three.
The Covenant launched an attack against the system in hopes to retrieve a Forerunner artifact that was in a museum on the planet's surface in 2552. The entire city was destroyed when the Spartans detonated a HAVOK Nuclear Warhead to level the city in order to prevent the Covenant from finding anything else of value. However, the planet remains in Human hands.
