In February 98 AD, Hadrian travelled from Moguntiacum (Mainz) to Colonia Agrippinensis (Cologne) to inform Trajan, the then governor of Germania Inferior, of the death of his adoptive father Nerva (who had died on 27 January) and to congratulate him on his accession to the imperial throne.
Hadrian’s first visit to the German provinces as emperor began in the early autumn of 121 AD. He spent the winter inspecting the armies and the Limes, organising troop placements and implementing extensive army reforms. In Colonia Agrippinensis (Cologne), Hadrian probably stayed with his close friend, Aulus Platorius Nepos, the then governor of Germania Inferior. Nepos was to accompagny Hadrian to Britain a few months later, when he was made governor of Roman Britain and oversaw the construction of Hadrian’s Wall.
More than a decade later, between 134 and 138 AD, Hadrian’s tour of the German provinces was commemorated on the imperial coinage (see here).
Source: Hadrian: The Restless Emperor – Anthony R. Birley