A new study suggests that medieval stone discs found in Ukraine were likely used by Vikings as solar compasses to navigate the seas. These discs, composed of the mineral pyrophyllite and dating between the 12th and 13th centuries, may have been navigational tools that helped Vikings chart their voyages. Researchers compared the pyrophyllite discs with other artifacts identified as navigational instruments used by Vikings and found similarities. The discs were most likely local products made in workshops near the city of Ovruch, and the origin of the raw material suggests local manufacturing. Further studies and archaeological experiments are needed to confirm the practical navigational purpose of these discs.