Black magical screens along the trench parapet, all crafted by a single fabricator mage, serving as periscopes.
Groups of black magical screens dot the Southern Front trench positions — basically magical periscopes that look like little porthole windows but are really just screens. All of them are the work of a single mage, a fabricator, who has since been reassigned to the Northern Front; if the periscopes break or are damaged, the defenders will have to peer over the trench lip the old-fashioned way.
Soldiers hunch over them for hours on end, a posture Carl notes as uncomfortable enough to warrant a mental note about adjusting their height. Princess Donut removes her sunglasses to look through one and praises the resolution as far better than the television Carl kept in his living room. Carl's own periscope is cracked and useless after the buried explosive line goes off.
Small black porthole-like screens set into the trench parapet, showing a magnified view of no-man's-land.
The trench line's only safe means of observing no-man's-land, and a single point of failure with their maker gone north.