Alcalá de Henares has a long history dating back to Roman times when it was called Complutum. It was influenced by Muslims in the 9th century when they built a castle. In the Middle Ages, it became an important trading city protected by walls. The Renaissance saw urban transformations under Archbishop Cisneros who founded the University of Alcalá. Although the Baroque period was economically difficult, culture thrived with theaters built. Modern times brought economic development, restoration of historic sites, and designation as a UNESCO World Heritage Site.