Bare-nosed wombats can excrete four to eight scat pieces at a time and may poop up to 100 cubes a day. After the wombat defecates, the furry critter collects the two centimeter-sized cubes and places them around their territory, possibly to communicate with other wombats or attract mates, reports George Dvorsky for Gizmodo.
I imagine it depends on whether the opposite gender finds walls sexy or not. I don't have a good feel for wombat aesthetics. Maybe they're into pyramids.
EDIT: This looks more like Stonehenge-level construction than Great Wall of China stuff going on: