The Limes Germanicus (Latin for Germanic frontier) was 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. At its height, the limes stretched from the North Sea outlet of the Rhine to near Regensburg on the Danube. Those two major rivers afforded natural protection from mass incursions into imperial territory, with the exception of a gap stretching roughly from Mogontiacum (Mainz) on the Rhine to Castra Regina (Regensburg) on the Danube.

The Limes Germanicus was divided into:

The total length was 568 km (353 mi). It included at least 60 forts and 900 watchtowers. The potentially weakest, hence most heavily guarded part of the Limes was the gap between the westward bend of the Rhine at modern-day Mainz and the main flow of the Danube at modern-day Regensburg. This 300-km wide land corridor between the two great rivers permitted movement of large groups of people without the need for water transport, hence the heavy concentration of forts and towers there, arranged in depth and in multiple layers along waterways, fords, roads, and hilltops.

Germanicus Julius Caesar (24 May 15 BC – 10 October AD 19), commonly known as Germanicus, was a member of the Julio-Claudian dynasty and a prominent general of the early Roman Empire. He was born in Rome, Italia, and was named either Nero Claudius Drusus after his father or Tiberius Claudius Nero after his uncle. He received the agnomen Germanicus in 9 BC, when it was posthumously awarded to his father in honour of his victories in Germania.

His own campaigns in Germania made him famous after avenging the defeat at the Battle of the Teutoburg Forest and retrieving the legion's eagles lost during the battle. Germanicus was the grandson-in-law and great-nephew of the Emperor Augustus, nephew and adoptive son of the Emperor Tiberius, father of the Emperor Caligula, brother of the Emperor Claudius, and the maternal grandfather of the Emperor Nero.

Germanicus was born in Rome in 15 BC. His parents were the general Nero Claudius Drusus (son of Empress Livia Drusilla, third wife of Emperor Augustus) and Antonia Minor (the younger daughter of the triumvir Mark Antony and Octavia Minor, sister of Augustus). Livilla was his younger sister and the future Emperor Claudius was his youngest brother.

Marcus Aurelius (Latin: Marcus Aurelius Antoninus Augustus; 26 April 121 – 17 March 180 AD), was Roman Emperor from 161 to 180 AD. He ruled with Lucius Verus as co-emperor from 161 until Verus' death in 169. He was the last of the "Five Good Emperors", and is also considered one of the most important Stoic philosophers. During his reign, the Empire defeated a revitalized Parthian Empire; Aurelius' general Avidius Cassius sacked the capital Ctesiphon in 164. Aurelius fought the Marcomanni, Quadi, and Sarmatians with success during the Marcomannic Wars, but the threat of the Germanic tribes began to represent a troubling reality for the Empire. A revolt in the East led by Avidius Cassius failed to gain momentum and was suppressed immediately.

Marcus Aurelius' Stoic tome Meditations, written in Greek while on campaign between 170 and 180, is still revered as a literary monument to a philosophy of service and duty, describing how to find and preserve equanimity in the midst of conflict by following nature as a source of guidance and inspiration.