Short answers, pulled from the story.
Italica was founded in 206 BC by the Roman general Publius Cornelius Scipio during the Second Punic War. He established it as a settlement for his Italic veterans and named it after them. It was the first Roman city built in Spain.
Trajan and Hadrian were both born in Italica. Some ancient authors also identify Italica as the birthplace of the emperor Theodosius I. Trajan and Hadrian were connected by adoption: Hadrian was Trajan's adopted son and successor.
The Traianeum was a large temple built by Hadrian to honour his adopted father and predecessor, the emperor Trajan. It measured 108 by 80 metres and occupied the highest point of the nova urbs. Its porticoed square was lined with more than a hundred columns of Cipollino marble from the Greek island of Euboea.
Italica's amphitheatre was the third largest in the Roman Empire at the time it was built, and it seated 25,000 spectators. That is roughly half the capacity of the Colosseum in Rome. The city's own population was estimated at only around 8,000 people, making the amphitheatre a deliberate display of status for the wider region.
Italica began to decline in the 3rd century AD when the Guadalquivir River shifted its course, leaving the city's river port stranded on dry land. The shift was probably caused by siltation following the removal of forest cover. The neighbouring city of Hispalis, modern Seville, continued to grow beside the active river channel.
A Royal Order of 1912 declared Italica a National Monument. The archaeological site's boundaries and protected zones were not formally defined until 2001. The first legal protection came much earlier, in 1810, under the Napoleonic occupation of Spain.