Throughout the streets of the city of Leiden in the Netherlands there are large hexagonal stones embedded into the ground, and while today the Leiden Stones (Red, White, and Blue), no longer carry much meaning, they once divided the city into different districts.
The Red Stone is a hexagonal sandstone block dating from the early 14th century which is embedded into the ground of the Haarlemmerstraat shopping district. Historically it had two functions, namely as a border between two parishes and as a central spot for practicing public law.
About the source: Atlas Obscura
Atlas Obscura aims 'to inspire wonder and curiosity about the incredible world we all share'. You can contribute to their collection on their website.