The Pierres du Niton (French for Neptune's Stones) are two unusual rocks which are visible from Quai Gustave-Ador in the harbor of Lake Geneva, Switzerland. They are remnants from the last ice age, left by the Rhone glacier. The Repère Pierre du Niton is the name of the rock which is bigger and further from the shore.
Guillaume-Henri Dufour used the Repère as a height starting point by the development of the Dufourmaps from 1845 to 1864 in the graduation 1:100 000. At that time the height over sea level was estimated and decreed to be 376.86 m. Up to today, this stone forms the authoritative point of the Swiss height measurement system. However, the height was newly evaluated in 1902 to be 373.6 m over sea level. This is why the data in maps of Switzerland made before 1902 differ by 3.26 m from today's official values.
In the Bronze Age, these stones likely had a spiritual significance and were used in religious ceremonies. This has been hypothesized due to square holes at the top of the larger stone, discovered in 1660, which seem to have been hewed by Middle Bronze Age (ca. 1500-1200 BC) axes.