Cote d'Azure
From Halopedia, the Halo wiki
Cote d'Azure was a planet mentioned in a seminar by Professor Anders. She stated that the planet had "large-scale engineered features", suggesting a possible presence of Forerunner structures on the planet.[1]
The colony was one of the first eight to be destroyed by the Covenant, being destroyed sometime in the first four years of the Human-Covenant War.