"In Germany construction or renovation of camps, fortifications, and roads detained me for nearly a year"

Hadrian is referring here to the Limes Germanicus, the line of fortifications and watch-towers which marked the eastern limits of the Roman Empire in Europe, from Katwijk in the Netherlands to Kolheim on the Danube. These defensive works were first put in place by Augustus, following the catastrophic defeat of the legions in the Battle of the Teutoberg Forest in 9 AD, and were augmented by subsequent emperors, including Hadrian and (perhaps more significantly), his successor, Antoninus Pius.

Map of the Limes Germanicus
GNU Free Documentation LicenseMap of the Limes Germanicus - Credit: Sansculotte

Reconstructed watchtower on the Limes Germanicus at Hillscheid, Germany
Public DomainReconstructed watchtower on the Limes Germanicus at Hillscheid, Germany - Credit: Schwing