The maps were previously £8.50 to download for the 4 maps but as of tomorrow (03/09/2007) this will be completely free to download directly through Xbox live Marketplace, so make sure you download it if you haven't already got it.
The Gears of War Hidden Fronts map pack, a collection of four add-on multiplayer areas for the Xbox 360 shooter, will be available for free beginning Sept. 3, Microsoft announced Friday.
The map pack was released as a paid download on May 3 and includes Bullet Marsh, a Kryll-infested swamp; Garden, a crumbling conservatory; Process, an underground factory; and Subway, a bombed-out commuter hub.
According to Microsoft, Gears is still the most popular game on Xbox Live, pulling in the highest number of unique players among all games on the system in August.
Hope that helps. :)