Complex sentence: A few years later it became the centre of the Roman fortifications along the Danube from Vindobona (Vienna) to Brigetio (Ó-Szőny), and (under Trajan or Hadrian) the permanent quarters of Legio XIV "Gemina".
Split into simpler sentences: A few years later it became the centre of the Roman fortifications along the Danube from Vindobona (Vienna) to Brigetio (Ó-Szőny). Under Trajan or Hadrian, Carnuntum became the permanent quarters of Legio XIV "Gemina".