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The borders of the Roman Empire

A map of the Roman Empire in 117 at the time of its greatest expansion at the death of Emperor Trajan

Between about 100 to 200 AD, during the time of the emperors from Trajan to Septimius Severus, the Roman Empire was at its largest. Back then, its borders ran across more than 20 present-day countries on three continents, for a total length of 7,500 kilometres.

Depending on local conditions, the border consisted of natural barriers - such as rivers, deserts or the sea - and man-made fortifications. Many sections of the overall border are still evident today, either above or below ground.

Taken together, the borders of the erstwhile Roman Empire immediately meet three of the make-or-break criteria for recognition as a World Heritage Site: They are a unique example of military architecture that has never existed before or since in human history. 

They are an extraordinary testimony to a lost civilisation that has never stopped shaping us. Along with the civilian settlement areas, they reflect a productive exchange of cultural values.

Due to their outstanding significance, all parts of the Roman Limes are going to be put, in the long term, on the UNESCO World Heritage List as ‘Frontiers of the Roman Empire’. They will be joining Hadrian's Wall (1986) and the Antonine Wall (2008) in Britain and the Upper Germanic-Raetian Limes (2005) in south-west Germany.

In summer 2021, the Danube Limes and the Lower Germanic Limes were also recognised as UNESCO World Heritage Sites.

A photo of the reconstructed Roman watchtower in Neuss-Reckberg
What does "Limes" actually mean?

Limes (plural: limites) is a Latin word that probably developed from the terms limus = across or limen = threshold. Initially, "limes" referred to spatial divisions in general, such as property boundaries, paths or lanes. 

Since Iulius Caesar, the term "limes" has also been used in connection with military operations, such as forest lanes in enemy territory. In his writing "Germania" (around 100 AD), the Roman historian Tacitus already uses the word "limes" to refer to "dry", i.e. land borders, in contrast to "ripa" (Latin: bank) for "wet", i.e. river borders. Today, the term "limes" refers to a section of the military border security system of the Roman Empire. 

Is the Limes a river?

In the north of the Roman Empire, the limes ran in large parts along the rivers Rhine, Main and Danube. These "wet borders" were secured by a chain of forts and legion camps. Sections of the Lower Germanic Limes, the Upper Germanic-Raetian Limes and parts of the Danube Limes were situated in what is today Germany. 

Limes sections in Germany
The Lower Germanic Limes

The Lower Germanic Limes was an important border section of the Roman Empire.

It followed the ancient course of the Rhine and stretched for about 400 kilometres between Katwijk (NL) on the North Sea to Bad Breisig in Rhineland-Palatinate. 

Some of the most important military bases and civilian centres of the Lower Germanic Limes were situated along the approximately 230-kilometre-long border section in what is now North Rhine-Westphalia.

The archaeological sites of the Lower Germanic Limes illustrate how borders developed in the Roman Empire and provides insight into life and culture in the frontier areas. 

A map of the sites along the Lower Germanic Limes

For this reason, the Kingdom of the Netherlands and the German states of North Rhine-Westphalia and Rhineland-Palatinate submitted a joint application for recognition of the Lower German Limes as a UNESCO World Heritage Site in January 2020.  In summer 2021, this application was positively decided. This section of the border is thus also part of the already existing serial and transnational UNESCO World Heritage Site "Frontiers of the Roman Empire".

A map of south-west Germany at the end of the 2nd/beginning of the 3rd century AD.
The Upper Germanic-Raetian Limes

The Upper Germanic-Raetian Limes served to protect the border the Roman provinces of Upper Germania and Raetia shared with free Germania. 

It protected only a comparatively short stretch of the northern border of the Roman Empire, but its remains, with a total length of 548 kilometres, are today the longest archaeological monument in Germany. 

The Upper Germanic-Raetian Limes ran from Rheinbrohl on the Rhine to Eining on the Danube and was laid out as straight as possible.

Today, the Upper Germanic-Raetian Limes runs through the states of Baden-Württemberg (164 km), Bavaria (158 km), Hesse (152 km) and Rhineland-Palatinate (75 km), and parts of it are still clearly visible.

The Upper Germanic-Rhaetian Limes was constructed in several phases from 100 AD onwards. Along its entire length there were over 900 watchtowers, built first from wood and later from stone. In addition, the border was reinforced by more than 60 forts.

The Upper Germanic Limes (length 382 km) consisted of palisade fencing several metres tall and consisting of sharpened logs.  Eventually berms and ditches were added in front. For about 50 kilometres, the Main River formed a section of the border.  Forts were put up to provide extra protection for this natural obstacle. 

From the beginning of the 3rd century AD, the Rhaetian Limes (length 166 km) consisted of a stone wall almost 3 metres tall and about 1 metre strong.  This was preferred over timber in order to better repel attacks by the Alemanni (a Germanic tribe). 

Since 2005, the Upper Germanic-Raetian Limes has been a UNESCO World Heritage Site and is thus part of the transnational World Heritage Site, ‘Frontiers of the Roman Empire’. 

A drawing of the development phases of the Roman limes on the northern borders: 1. forest aisle with post road (1st century AD), 2. wooden tower with post road (early 2nd century AD), 3. wooden stone tower with military road and palisade (mid 2nd century), 4. stone tower with wall and military road (Raetia/Britain, late 2nd century), 5. stone tower with military road, earth wall and ditch (2nd to 3rd century).  Translated with (free version)
The Danube Limes

Like the Lower Germanic Limes, the "Danube Limes" border section was a river border and ran along the Danube in modern-day Bavaria, Austria, Slovakia, Hungary, Serbia, Romania and Bulgaria. 

Unlike with the Upper Germanic-Rhaetian Limes, the impenetrable terrain alongside the Danube made linear border fortifications unnecessary. However, from the 1st century AD onwards, the river border was given extra protection by adding watchtowers, legion camps and forts. Emperor Trajan did his best to have the earthen ramparts of the legion’s camps replaced by stone walls.