Box Forts
From Halopedia, the Halo wiki
A box fort, as the name implies, is using crates, and loose objects found in many Halo 2 multiplayer maps and placing them strategically so that you may have the advantage over your enemies. It is best used on the map Foundation on the game types Zombie and CTF. The two positions are hanger number two, and number four; number two being better because it is harder for the zombies to move the metal legs. The other examples of box forts would be blocking the two front doors on Zanzibar in CTF or using the large boxes on Waterworks to block the ramps at the bases
Halo 3
In Halo 3 using Forge it is possible to make even more elaborate Box forts. An example would be using crates on High Ground to completely block off the base to the outside
