Last Saturday, I visited the archeological park at Xanten or Colonia Ulpia Traiana. It covers large parts of the original settlement and various buildings have been reconstructed. The original city almost completely vanished, while it was used as a query for building the modern city. The amphitheater is an almost exact copy of the ancient building. More pictures can be found here!
Around 15 BC the Roman camp Castra Vetera was created on the Fürstenberg near today's locality Birten. It was intended as a base for campaigns into Germania and until its destruction during the Revolt of the Batavi in 70 AD it was occupied by 8,000 to 10,000 legionaries, and was the main base of the Classis germanica.
After the destruction of Castra Vetera a second camp became established at the Bislicher Insel, named Castra Vetera II, which became the base camp of Legio VI Victrix. A nearby created settlement, which was inhabited by 10,000 to 15,000 usually former legionaries, was given the rights of a Colonia in 110 by the Roman emperor Marcus Ulpius Traianus, who renamed the city into Colonia Ulpia Traiana. The colonia became the second most important commercial post in the province of Germania Inferior, only surpassed by Colonia Agrippinensis (today's Cologne). In 122, Vetera II became the camp of Legio XXX Ulpia Victrix, which substituted VI Victrix which had moved to Britannia.