Although it has long been known that the sphere of our Earth flattens at the poles, its precise measurements were still uncertain in the early 19th century. More accurate data was needed to support co-ordinate systems as well as for military purposes. Baltic-German astronomer Friedrich George Wilhelm Struve and Russian Army General Carl von Teller received funding from Czar Alexander I and Prince Volkonsky to carry out their ambitious plan to establish a chain of survey triangulations on the western border of Russia. Swedish astronomers joined the effort later. Called the Struve Geodetic Arc, this triangulation chain extends from the Black Sea in the Ukraine to a point near Hammerfest, Norway.
258 Triangles and 265 Points in Ten Countries
Surveying for the Struve Geodetic Arc began in 1816 and was completed 39 years later. The chain consists of 258 main triangles, 265 main station points and 60 sub-station points. At the time of its founding, the Arc passed through Russia and Sweden. Today, however, its station points are found in ten countries: Norway, Sweden, Finland, Russia, Estonia, Latvia, Lithuania, Belarus, Moldova and the Ukraine.
The survey was an enormous undertaking. The Arc is nearly 3,000 kilometres long, and physical access to many of the locations was very poor at that time. Surveyors were forced to travel on foot, skis, horseback, reindeer and boats. There were no decent maps or aerial photos to help in defining the topography. At the main station points, holes were drilled into the bedrock, filled with lead and topped by a brass plaque. Each and every measurement taken was painstakingly documented and published in a three-volume record of the survey.
Gaining World Heritage Site Status
The Struve Geodetic Arc was inscribed as a World Heritage Site in 2005. The Arc is the first World Heritage Site that passes through so many countries. The Struve Geodetic Arc differs from other World Heritage Sites in that it cannot actually be seen. Indeed, its importance has nothing to do with offering a spectacular sight to see - the Arc is an impressive scientific achievement and showcase of surveying prowess. The extremely precise survey results served a basis for future surveying work.
The inscribed site includes 34 of the original station points, six of which lie in Finland. In addition to Svartvira (now called Mustaviiri), which is located in the Pyhtää Archipelago in the eastern part of the Gulf of Finland National Park, the following Arc station points have been inscribed in Finland: Stuor-oivi (Stuorrahanoaivi) near the Norwegian border in the Tarvantovaara Wilderness Area, Avasaksa (Aavasaksa), Tornea (Alatornio Church) in Western Lapland, Puolakka (Oravivuori) in Korpilahti, and Porlom II (Tornikallio) in Porlammi, Lapinjärvi.
Mustaviiri, Aavasaksa and Stuorrahanoaivi
The station points Mustaviiri, Aavasaksa and Stuorrahanoaivi are in areas administered by Metsähallitus. The northernmost of these points is located on the "arm" of Finland at the summit of Stuorrahanoaivi, which lies close to the Norwegian border. The first station point at the summit was surveyed in 1850 and the second in 1852. Both were marked by crosses carved into the bedrock. At the end of the 19th century the second surveyed point was replaced with a more prominent center peg marker. There are no roads leading to Stuorrahanoaivi. A trail leading to Salvasjärvi is the closest route to the station point. From Salvasjärvi, it is another ten kilometres' hike to the station point. The station point can also be reached on an ATV trail that runs through Syväjärvi.
The Aavasaksa station point was set in 1845 on a fell summit site with the best vantage point and marked by carving a cross in the bedrock. Unfortunately, the original marker was covered by an observation tower built in 1969. The shape of the Earth was surveyed at Aavasaksa in the 1730s, when French astronomer and mathematician Pierre Louis Moreau de Mapertuis and his expedition surveyed the area. The Aavasaksa summit can be reached by car.
Mustaviiri, which is located in the eastern part of the Gulf of Finland National Park, is found on a small, rocky islet. The station point is marked by a small hole approximately the size of a matchbox drilled into the bedrock. It is Finland's southernmost World Heritage Site station point. It was surveyed in 1833. The Mustaviiri station point can be reached by a trail from the harbour.
Mustaviiri and Stuorrahanoaivi were made main station points in surveys conducted for the Struve Geodetic Arc.
There are dozens of Arc station points not included in the World Heritage Site; a total of 83 were surveyed in Finland. One might try to locate these station points at, for example, the Ala-Penikka hill in Simos, at Hiukkavaara in Oulu or Kylmäkangas in Kuhmoinen. Even though these are not part of the World Heritage Site, they are also protected under the Antiquities Act.