Blessed Bulwark

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.

Source
pg. 123
 * Warhammer Fantasy Battles (8th Edition)