The Struve Geodetic Arc crosses 10 countries as a UNESCO World Heritage Site.
The arc is a chain of survey points stretching for more than 2,800 kilometres from near the Norwegian Sea to the Black Sea. Astronomer Friedrich Georg Wilhelm Struve organized the measurements between 1816 and 1855 to determine the size and shape of Earth more accurately.
Surveyors measured a long meridian arc using triangulation. The project helped establish the length of a degree of latitude and provided important evidence that Earth is slightly flattened at the poles rather than a perfect sphere.
The original network contained 265 main station points, but UNESCO’s serial property includes 34 monuments marking selected points. The countries represented are Norway, Sweden, Finland, Russia, Estonia, Latvia, Lithuania, Belarus, Ukraine, and Moldova. A common mistake is to count the original survey points instead of the countries crossed.