From Halopedia, the Halo wiki
Xanadu was one of seven provincial regions of Mu, itself one of six continents on the human Outer Colony planet, Arcadia.
Xanadu comprised the mid-southern portion of Mu and was bordered by Perseopolis, Sarai, Abaskun, and New Troy. On September 9, 2549, the Covenant glassed the region along with the rest of the planet.
Xanadu was the capital of Kublai Khan's Yuan dynasty in China.