of the Spanish Inquisition was instituted in Seville in 1478. Its primary charge was to ensure that all nominal Christians were really behaving like Christians, and not practicing what Judaism they could in secret. At first, the activity of the Inquisition was limited to the dioceses of Seville and Córdoba, where the Dominican friar, Alonso de Ojeda, had detected converso activity. The first Auto de Fé took place in Seville on 6 February 1481, when six people were burned alive. Alonso de Ojeda himself gave the sermon. The Inquisition then grew rapidly. The Plaza de San Francisco was the site of the 'autos de fé'. By 1492, tribunals existed in eight Castilian cities: Ávila, Córdoba, Jaén, Medina del Campo, Segovia, Sigüenza, Toledo, and Valladolid; and by the Alhambra Decree all Jews were forced to convert to Catholicism or be exiled (expelled) from Spain. Early modern period Following the Columbian exploration of the New World, Seville was chosen as headquarters of the Casa de Contratación in 1503, which was the decisive development for Seville becoming the port and gateway to the Indies. Unlike other harbours, reaching the port of Seville required sailing about up the River Guadalquivir. The choice of Seville was made in spite of the difficulties for navigation in the Guadalquivir stemming from the increasing tonnage of ships as a result of the relentless drive to make maritime transport cheaper during the late Middle Ages. Nevertheless, technical suitability issues notwithstanding, the choice was still reasonable in the sense that Seville had become the largest demographic, economic and financial centre of Christian Andalusia in the late Middle Ages. A 'golden age of development' commenced in Seville, due to its being the only port awarded the royal monopoly for trade with the growing Spanish colonies in the Americas and the influx of riches from them. Since only sailing ships leaving from and returning to the inland port of Seville could engage in trade with the Spanish Americas, merchants from Europe and other trade centres needed to go to Seville to acquire New World trade goods. The city's population grew to more than a hundred thousand people. In the late 16th century the monopoly was broken, with the port of Cádiz also authorised as a port of trade. Throughout the 17th century, colonial trade declined. Spain's American Colonies improved their production of basic goods, reducing their need to import. Compounded with these