Limes Rampart in the Taunus

Limes (Latin originally "Querweg", "Schneise", especially "Grenzweg" in connection with the division of an area or the development of a site, later generally "Border"; [1] plural limites) denotes the Roman Empire from 1. Border walls built up to the 6th century AD or military border security systems in Europe, the Middle East and North Africa. It is also used for later comparable border drawing (Limes Saxoniae) or monitoring systems at imperial borders. The term is originally derived from the Latin words limus "quer" and limen "door threshold". Initially, the Romans only understood this term to be a field or a field, which was delimited with boundary stones (termini), wooden posts or clearly recognizable landmarks (trees, rivers). From the time of Gaius Julius Caesar, military roads with fortified sentries and marshals on a forest aisle (see also below) or quickly laid out roads in enemy territory were called Limes.

Here you can see the course of the Limes really well.

There's a lot of history here