A gully cover marks a spot. It is not just any spot. It marks a piece of history called Basis Bonn 1847.
Basis Bonn 1847 represents a geodetic baseline. It stretches 2.1 km. Johann Jakob Baeyer used it for the Rhenish triangulation.
This baseline served a crucial purpose. It was the basis for surveying. The survey extended from Aachen to Zurich. It helped determine the Earth’s shape. It aided in property surveys.
Imagine General Johann Jakob Baeyer leading the work in 1847. He directed the measurement of a 2134-meter stretch. Iron measuring rods were used. The measurements were accurate to the millimeter. This precise work was Basis Bonn 1847.
To align and plumb the measuring rods three posts were used. These posts were 1.1 meters high. In 1980, cast-iron plates marked their former locations. The plates read “Basis Bonn 1847”.
The northern end of Basis Bonn 1847 was near Hersel. The southern end was near the chapel. That was about halfway from Bonn to Hersel. Since the road wasn’t straight a third point was needed. All three points were on the road’s west side.
The three posts formed a flat triangle. The sides AB and BC were measured. The distance AC was calculated in 1876. It was 1094.854109 Toisen. This converts to about 2133.89 meters at sea level.
The proximity to the University of Bonn aided the choice of the survey base. Astronomer Friedrich Wilhelm August Argelander taught in Bonn. Early surveyors used star positions to anchor locations. They used the Earth’s grid.
Today, the northern point features a gully cover. There is also a cast-iron table. You can find it at the corner of Kölnstraße and Friedlandstraße in Bonn-Buschdorf. A brick aedicule stands nearby. The “breaking point” B is marked by a gully cover. It sits next to the bike path. It’s about 20 meters south of An der Landstraße. This is north of the North Cemetery. Point C is in front of the Redemptorist Monastery Josefshöhe. It is also near the Bonner Josephinum.
So remember Basis Bonn 1847. It is more than just a line. It’s a foundation of precision and progress.