Limes (Roman Empire) in the context of "Justiniana Prima"

The Limes Germanicus (Latin for Germanic frontier), or 'Germanic Limes', is the name given in modern times to a line of frontier (limes) fortifications that bounded the ancient Roman provinces of Germania Inferior, Germania Superior and Raetia, dividing the Roman Empire and the unsubdued Germanic tribes from the years 83 to about 260 AD. The frontier used either a natural boundary such as a river or typically an earth bank and ditch with a wooden palisade and watchtowers at intervals, and a system of linked forts was built behind them.

The path of the limes changed over time following advances and retreats due to pressure from external threats. At its height, the Limes Germanicus stretched from the North Sea outlet of the Rhine to near Regensburg (Castra Regina) on the Danube. These two major rivers afforded natural protection from mass incursions into imperial territory, with the exception of a gap stretching roughly from Mogontiacum (now Mainz) on the Rhine to Castra Regina.

The Suebi (also spelled Suevi or Suavi) were a large group of Germanic peoples first reported by Julius Caesar in the 1st century BC. In different contexts over several centuries, peoples within this umbrella category were sometimes simply called the Suebi, although all or most Suebian peoples had their own names as well. They originated near the Elbe River in what is now Eastern Germany. From there, Suebian groups spread across Central Europe, and in the 5th and 6th centuries some took over parts of Spain, Portugal and Italy. Archaeologically, the forerunners of the Suebi before contact with Rome are associated with the Jastorf culture. During the Roman imperial period the Suebi are associated with the so-called "Elbe Germanic peoples" who brought Elbe material culture into new areas to the south and southwest. Linguistically, although contemporary evidence for Roman-era Suebian language is scarce, they spoke a Germanic language, which is believed to be the main predecessor of medieval Old High German, and the modern German language, with all its related dialects.

With the advent of Roman dominance in the 1st and 2nd centuries AD, some Suebi moved into Roman controlled regions near the Neckar river, while a powerful Suebian alliance outside their control maintained a tense relationship with the Roman empire. This was led by the Marcomanni, who settled with other Suebi in remote forests and mountains north of the Roman border along the Danube river, and maintained connections with Suebian and non-Suebian peoples to their north. After their crushing defeat to the Romans in the Marcomannic Wars of the late 2nd century, many Suebi moved into the Roman Empire, or regrouped in areas near the Roman frontier. Notably, the diverse group who came to be known as the Alemanni, took control of Roman territory in what later became medieval Swabia - a cultural region in southern Germany that still bears a version of the Suebian name. During the 3rd and 4th centuries, the Romans were often raided by the Alemanni, Juthungi, Quadi and other Suebi, and attempts to subjugate them had limited success.

Tiberius Julius Caesar Augustus (/taɪˈbɪəriəs/ ty-BEER-ee-əs; 16 November 42 BC – 16 March AD 37) was Roman emperor from AD 14 until 37. He succeeded his stepfather Augustus, the first Roman emperor. Tiberius was born in Rome in 42 BC to Roman politician Tiberius Claudius Nero and his wife, Livia Drusilla. In 38 BC, Tiberius's mother divorced his father and married Augustus. Following the untimely deaths of Augustus's two grandsons and adopted heirs, Gaius and Lucius Caesar, Tiberius was designated Augustus's successor. Prior to this, Tiberius had proved himself an able diplomat and one of the most successful Roman generals. His conquests of Pannonia, Dalmatia, Raetia, and (temporarily) parts of Germania laid the foundations for the empire's northern frontier.

Early in his career, Tiberius was happily married to Vipsania, daughter of Augustus's friend, distinguished general and intended heir, Marcus Vipsanius Agrippa. They had a son, Drusus Julius Caesar. After Agrippa died, Augustus insisted that Tiberius divorce Vipsania and marry Agrippa's widow, Augustus' own daughter (Tiberius's step-sister) Julia. Tiberius reluctantly gave in. This second marriage proved scandalous, deeply unhappy, and childless; ultimately, Julia was sent into exile by her father. Tiberius adopted his nephew, the able and popular Germanicus, as heir. On Augustus's death in 14, Tiberius became princeps at the age of 55. He seems to have taken on the responsibilities of head of state with great reluctance and perhaps a genuine sense of inadequacy in the role, compared to the capable, self-confident and charismatic Augustus.

The barbarian invasions of the third century (212–305) constituted an uninterrupted period of raids within the borders of the Roman Empire, conducted for purposes of plunder and booty by armed peoples belonging to populations gravitating along the northern frontiers: Picts, Caledonians, and Saxons in Britain; the Germanic tribes of Frisii, Saxons, Franks, Alemanni, Burgundians, Marcomanni, Quadi, Lugii, Vandals, Juthungi, Gepids and Goths (Tervingi in the west and Greuthungi in the east), the Dacian tribes of the Carpi and the Sarmatian tribes of Iazyges, Roxolani and Alans, as well as Bastarnae, Scythians, Borani and Heruli along the Rhine-Danube rivers and the Black Sea.

Since the time of Marcus Aurelius during the Marcomannic Wars (166/167-189), Germanic-Sarmatian tribes had not exerted such strong pressure along the northern borders of the Roman Empire.

The Limes Arabicus was a desert frontier of the Roman Empire, running north from its start in the province of Arabia Petraea. It ran northeast from the Gulf of Aqaba for about 1,500 kilometers (930 mi) at its greatest extent, reaching northern Syria and forming part of the wider Roman limes system. It had several forts and watchtowers.

The reason of this defensive limes was to protect the Roman province of Arabia from attacks of the nomadic tribes of the Arabian desert. The main purpose of the Limes Arabicus is disputed; it may have been used both to defend from Arab raids and to protect the commercial trade routes from robbers.

The crossing of the Rhine by a mixed group of barbarians which included Vandals, Alans and Suebi is traditionally considered to have occurred on 31 December 406. The crossing transgressed one of the Late Roman Empire's most secure limes or boundaries; as such, it has been considered a climactic moment in the decline of the empire. It initiated a wave of destruction of Roman cities and the collapse of Roman civic order in northern Gaul. That, in turn, occasioned the rise of three usurpers in succession in the province of Britannia. Therefore, the crossing of the Rhine is a marker date in the Migration Period during which various Germanic tribes moved westward and southward from southern Scandinavia and northern Germania.

The Sorbian March (Latin: limes Sorabicus, German: Sorbenmark, Upper Sorbian: Serbska marka, Lower Sorbian: Serbska marka) was a frontier district on the eastern border of East Francia in the 9th through 11th centuries. It was composed of several counties bordering the Sorbs. The Sorbian March seems to have comprised the eastern part of Thuringia.

The Sorbian March was sometimes referred to as the Thuringian March. The term "Sorbian March" appears only four times in the Annales Fuldenses.

The limitanei (Latin, also called ripenses), meaning respectively "the soldiers in frontier districts" (from the Latin word limes meaning frontier) or "the soldiers on the riverbank" (from the Rhine and Danube), were an important part of the late Roman and early Byzantine army after the reorganizations of the late 3rd and early 4th centuries. The limitanei, unlike the comitatenses, palatīni, and scholae, garrisoned fortifications along the borders of the Roman Empire and were not normally expected to fight far from their fortifications.

The limitanei were lower-status and lower-paid than the comitatenses and palatīnī, and the distinction in role and status between scholae, palatini, comitatenses, and limitanei had largely replaced the older one between praetorians, legionaries, and auxiliaries. The limitanei and palatini both included legionary units alongside auxiliary units.