Assembly
From Halopedia, the Halo wiki
Purple Reign is the nickname for a map that is announced in the Bungie Weekly Update: 10/26/2007 [1] . It will be available for download on Xbox Live Marketplace in the future.
It has been stated that it will be symmetrical or semi-symmetrical with the middle of the map being higher than the rest.[1] This has led to theories that it will be a Midship remake, as that map was symmetrical, had a raised area in the center, and has a purple color scheme.
The nickname is a reference to Prince's song and movie, Purple Rain.