It is common practice in the Empire for a Warrior Priest to bless any wall which might have to serve in the battle against the foul creatures of Chaos. Such enchantment lingers on long after it takes root, and even endures through the destruction of the wall itself. Many farming fields and fortress walls in the Empire are bounded by walls constructed of stolen fragments from the blessed bulwarks, and retain a portion of that power.
Blessed bulwarks are obstacles that grant hard cover to units behind them, and a -1 To Hit modifier to charging models in base contact with them. In addition to this, models from the Forces of Destruction (Allied Armies) that are in base contact with the obstacle must halve their Initiative.