fschmidt
The border between Saxony and Prussia is marked with numbered boundeary stones. For higher detail, there are unnumbered Läufersteine between the numbered stones which show "where the border runs" (wo die Grenze verläuft). So, it is a historic border with still existing boundary stones. I did not check how many boundary stones are still there, AFAIK the maintainer of openhistorymap has detailed knowledge on these stones.