The cathedral and the Alcazar in Seville have been declared UNESCO World Heritage Sites.  The Cathedral in Seville is the largest Gothic building in Europe.

Seville was the center of commerce with the Americas, but before that Seville had Arabic and Jewis past. The Pilatos palace, the Alcazar and the Juderia (Jewis village) are the site that you shouldn't miss.

Roman Seville:  At Carmona, you can visit a necropolis of 800 tombs from the time of the Romans.  Italica has a Roman museum, and the ruins of one of the larges arenas outside of Rome, as well as some remains of a Roman town.  The Archaeological Museum has a Mercury with winged sandals and a bust of the emperor Trajan.