Limes Germanicus in the context of "Trajan"

Flavius Valerius Constantius (c. 250 – 25 July 306), also called Constantius I, was a Roman emperor from 305 to 306. He was one of the four original members of the Tetrarchy established by Diocletian, first serving as caesar from 293 to 305 and then ruling as augustus until his death. Constantius was also father of Constantine the Great, the first Christian emperor of Rome. The nickname "Chlorus" (Ancient Greek: Χλωρός, lit. 'the Pale') was first popularized by Byzantine-era historians and not used during the emperor's lifetime.

As an Illyrian soldier of humble origin, Constantius had a distinguished military career and rose to the top ranks of the army. Around 289, he set aside Helena, Constantine's mother, to marry a daughter of Emperor Maximian, and in 293 was added to the imperial college by Maximian's colleague Diocletian. Assigned to rule Gaul, Constantius defeated the usurper Carausius there and his successor Allectus in Britain, and campaigned extensively along the Rhine frontier, defeating the Alamanni and Franks. When the Diocletianic Persecution was announced in 303, Constantius ordered the demolition of churches but did not actively hunt down Christians in his domain. Upon becoming senior emperor in May 305, Constantius launched a successful punitive campaign against the Picts beyond the Antonine Wall. He died suddenly at Eboracum (York) in July the following year.

Maximian (Latin: Marcus Aurelius Valerius Maximianus; c. 250 – c. July 310), nicknamed Herculius, was Roman emperor from 286 to 305. He was Caesar from 285 to 286, then Augustus from 286 to 305. He shared the latter title with his co-emperor and superior, Diocletian, whose political brain complemented Maximian's military brawn. Maximian established his residence at Trier but spent most of his time on campaign. In late 285, he suppressed rebels in Gaul known as the Bagaudae. From 285 to 288, he fought against Germanic tribes along the Rhine frontier. Together with Diocletian, he launched a scorched earth campaign deep into Alamannic territory in 288, refortifying the frontier.

The man he appointed to police the Channel shores, Carausius, rebelled in 286, causing the secession of Britain and northwestern Gaul. Maximian failed to oust Carausius, and his invasion fleet was destroyed by storms in 289 or 290. Maximian's subordinate Constantius campaigned against Carausius' successor, Allectus, while Maximian held the Rhine frontier. The rebel leader was ousted in 296, and Maximian moved south to combat piracy near Hispania and Berber incursions in Mauretania. When these campaigns concluded in 298, he departed for Italy, where he lived in comfort until 305. At Diocletian's behest, Maximian abdicated on 1 May 305, gave the Augustan office to Constantius, and retired to southern Italy.

Raetia or Rhaetia (/ˈriːʃ(i)ə/ REE-sh(ee-)ə, Latin: [ˈrae̯.ti.a]) was a province of the Roman Empire named after the Rhaetian people. It bordered on the west with the country of the Helvetii, on the east with Noricum, on the north with Vindelicia, on the south-west with Transalpine Gaul and on the south with Venetia et Histria, a region of Roman Italy.

It thus comprised the districts occupied in modern times by eastern and central Switzerland (containing the Upper Rhine and Lake Constance), southern Germany (Bavaria and most of Baden-Württemberg), Vorarlberg and the greater part of Tyrol in Austria, and part of northern Lombardy in Italy. The region of Vindelicia (today eastern Württemberg and western Bavaria) was annexed to the province at a later date than the others. The northern border of Raetia during the reigns of emperors Augustus and Tiberius was the River Danube. Later the Limes Germanicus marked the northern boundary, stretching for 166 km north of the Danube. Raetia was connected to Italy across the Alps over the Reschen Pass, by the Via Claudia Augusta.

The Flavian dynasty, lasting from 69 to 96 CE, was the second dynastic line of emperors to rule the Roman Empire following the Julio-Claudians, encompassing the reigns of Vespasian and his two sons, Titus and Domitian. The Flavians rose to power during the civil war of 69 CE, known as the Year of the Four Emperors; after Galba and Otho died in quick succession, Vitellius became emperor in mid 69. His claim to the throne was quickly challenged by legions stationed in the eastern provinces, who declared their commander Vespasian emperor in his place. The Second Battle of Bedriacum tilted the balance decisively in favor of the Flavian forces, who entered Rome on 20 December, and the following day, the Roman Senate officially declared Vespasian emperor, thus commencing the Flavian dynasty. Although the dynasty proved to be short-lived, several significant historic, economic and military events took place during their reign.

The reign of Titus was struck by multiple natural disasters, the most severe of which was the eruption of Mount Vesuvius in 79 CE, which saw the surrounding cities of Pompeii and Herculaneum be completely buried under ash and lava. One year later, Rome was struck by fire and a plague. On the military front, the Flavian dynasty witnessed the siege and destruction of Jerusalem by Titus in 70 CE, following the failed Jewish rebellion of 66. Substantial conquests were made in Great Britain under the command of Gnaeus Julius Agricola between 77 and 83 CE, while Domitian was unable to procure a decisive victory against King Decebalus in the war against the Dacians. In addition, the Empire strengthened its border defenses by expanding the fortifications along the Limes Germanicus.

Germania Superior ("Upper Germania") was an imperial province of the Roman Empire. It comprised an area of today's western Switzerland, the French Jura and Alsace regions, and southwestern Germany. Important cities were Besançon (Vesontio), Strasbourg (Argentoratum), Wiesbaden (Aquae Mattiacae), and Germania Superior's capital, Mainz (Mogontiacum). It comprised the Middle Rhine, bordering on the Limes Germanicus, and on the Alpine province of Raetia to the south-east. Although it had been occupied militarily since the reign of Augustus, Germania Superior (along with Germania Inferior) was not made into an official province until c. 85 AD.

The Upper Germanic-Rhaetian Limes (German: Obergermanisch-Raetischer Limes), or ORL, is a 550-kilometre-long section of the former external frontier of the Roman Empire between the rivers Rhine and Danube. It runs from Rheinbrohl to Eining on the Danube. The Upper Germanic-Rhaetian Limes is an archaeological site and, since 2005, a UNESCO World Heritage Site. Together with the Lower Germanic Limes it forms part of the Limes Germanicus.

The Limes used either a natural boundary such as a river or typically an earth bank and ditch with a wooden palisade and watchtowers at intervals. A system of linked forts was built behind the Limes.