Emperor Augustus considered conquest beyond the Rhine and the Danube not only regular foreign policy but also necessary to counter Germanic incursions into a still rebellious Gaul. A series of forts and commercial centers were established along the two rivers. Some tribes, such as the Ubii consequently allied with Rome and readily adopted advanced Roman culture. During the 1st century CE Roman legions conducted extended campaigns into Germania magna, the area north of the Upper Danube and east of the Rhine, attempting to subdue the various tribes. Roman ideas of administration, the imposition of taxes and a legal framework were frustrated by the total absence of an infrastructure. The campaigns of Germanicus, for example were almost exclusively characterized by frequent massacres of villagers and indiscriminate pillaging. The tribes, however maintained their elusive identities. In 9 AD a coalition of tribes under the Cherusci chieftain Arminius, who was familiar with Roman tactical doctrines, defeated a sizeable Roman force in the Battle of the Teutoburg Forest. Consequently, Rome resolved to permanently establish the Rhine/Danube border and refrain from further territorial advance into Germania. By AD 100 the frontier along the Rhine and the Danube and the Limes Germanicus was firmly established. Several Germanic tribes lived under Roman rule south and west of the border, as described in Tacitus's "Germania". These lands represent the modern states Baden-Württemberg, southern Bavaria, southern Hesse, Saarland and the Rhineland. Austria formed the regular provinces of Noricum and Raetia. The provinces Germania Inferior (with the capital situated at Colonia Claudia Ara Agrippinensium, modern Cologne) and Germania Superior (with its capital at Mogontiacum, modern Mainz), were formally established in 85 AD, after long and painful campaigns as lasting military control was confined to the lands surrounding the rivers.