Imperial Defence Line
Across the Imperium, mankind defends itself from the various gribblies and warp tentacles. The only thing standing between Your Dudes and being unceremoniously turned into mincemeat are the Imperial Defence Lines; a bulwark that can be used to resist the onslaught of such foes.
The Wall of Martyrs Imperial Defence Line consists of long, trench-like fortified platforms, and smaller fortifications, all of which come bedecked with a huge array of details including: the decaying bones of dead Cadians, abandoned weaponry, Imperial eagles and the iconography of the Imperium of Man. There are also ammunition crates, shovels, metal rivets and manholes. Despite this, it offers less overall protection than the Aegis Defence Line, although Death Korps of Krieg love these things in spades.
Basically, they're using the still armored corpses of dead Guardsmen to add extra protection.
Compared to the Aegis, the Imperial Defence Line trades the ability to take guns in favour of adding +1 Ld to Imperium Infantry, while also giving units behind it and not in it the benefit of cover.