Most starforts I've visited have at least a few of these curved granite pieces lying around. I'm pretty sure they were part of the fort's original design, for mounting the guns that were imagined would be used when the fort was complete...but starforts take so long to build that by the time a new fort was ready to mount its guns, gun technology had advanced, and different guns were available, necessiating different mounting strategies. Giant blocks of granite aren't anybody's favorite thing to relocate, so the leftovers are frequently found in untidy piles such as these. Tori is scandalized by such a fiendish disregard for building materials.