 The date of the division is unknown, most certainly after AD 20 but before AD 50.The proximity of dangerous barbarian tribes (Quadi, Marcomanni) necessitated the presence of a large number of troops (seven legions in later times), and numerous fortresses were built on the bank of the Danube.Some time between the years 102 and 107, between the first and second Dacian wars, Trajan divided the province into Pannonia Superior (western part with the capital Carnuntum), and Pannonia Inferior (eastern part with the capitals in Aquincum and Sirmium).