migrating or silting up. At present, the branches Waal and Nederrijn-Lek discharge to the North Sea through the former Meuse estuary, near Rotterdam. The river IJssel branch flows to the north and enters the IJsselmeer (formerly the Zuider Zee), initially a brackish lagoon but a freshwater lake since 1932. The discharge of the Rhine is divided into three branches: the Waal (6/9 of total discharge), the Nederrijn – Lek (2/9 of total discharge) and the IJssel (1/9 of total discharge). This discharge distribution has been maintained since 1709 by river engineering works including the digging of the Pannerdens Kanaal and the installation, in the 20th century, of a series of weirs on the Nederrijn. Military and cultural history Antiquity The Rhine was not known to Herodotus and first enters the historical period in the 1st century BC in Roman-era geography. At that time, it formed the boundary between Gaul and Germania. Although it is estimated that germanic tribes have been inhabiting the area since 2000 BCE. The Upper Rhine had been part of the areal of the late Hallstatt culture since the 6th century BC, and by the 1st century BC, the areal of the La Tène culture covered almost its entire length, forming a contact zone with the Jastorf culture, i.e. the locus of early Celtic-Germanic cultural contact. In Roman geography, the Rhine formed the boundary between Gallia and Germania by definition; e.g. Maurus Servius Honoratus, Commentary on the Aeneid of Vergil (8.727) (Rhenus) fluvius Galliae, qui Germanos a Gallia dividit "(The Rhine is a) river of Gaul, which divides the Germanic people from Gaul." In Roman geography, the Rhine and Hercynia Silva were considered the boundary of the civilized world; as it was a wilderness, the Romans were eager to explore it. This view is typified by Res Gestae Divi Augusti, a long public inscription of Augustus, in which he boasts of his exploits; including, sending an expeditionary fleet north of the Rheinmouth, to Old Saxony and Jutland, which he claimed no Roman had ever done before. Augustus ordered his stepson Roman general Drusus to establish 50 military camps along the Rhine, starting the Germanic Wars in 12 BC. At this time, the plain of the Lower Rhine was the territory of the Ubii. The first urban settlement, on the grounds of what is today Downtown Cologne, along the Rhine, was Oppidum Ubiorum, which was founded in 38