The Alcázar was involved in the civil war where Henry IV of Castile faced a rebellion that backed his teenage half-brother Alfonso. During the war, the Alcázar's defenses were upgraded to deal with the advent of gunpowder. At the same time, the Alcázar's main tower, now known as the "Tower of the Inquisition" was constructed. Henry's successor, Isabella and her husband, Ferdinand, used the Alcázar for one of the first permanent tribunals of the Spanish Inquisition and as a headquarters for their campaign against the Nasrid dynasty in Granada, the last remaining Moorish kingdom in the Iberian Peninsula. The Inquisition began using the Alcázar as one of its headquarters in 1482, converting much of it, including the Arab baths, into torture and interrogation chambers. The Inquisition maintained a tribunal here for three centuries. Boabdil was held prisoner here in 1483 until he promised to make Granada a tributary state. When Boabdil refused to surrender his kingdom in 1489, the Christians launched an attack. Isabella and Ferdinand's campaign against Granada succeeded in 1492. The same year, the monarchs met Christopher Columbus in the Alcázar as he prepared to take his first voyage to the Americas. The Alcázar served as a garrison for Napoleon Bonaparte's troops in 1810. In 1821, the Alcázar became a prison. Finally, the Spanish government made the Alcázar a tourist attraction and national monument in the 1950s. The outdoor area of the Alcázar is situated within the walls of the four towers (Paloma, Leones, Homenaje and Inquisición), this creating an almost square shape to the building. The main hall of the building, constructed in the 18th century, is referred to as the “Hall of Mosaics”, given the impressive Mosaics that can be found within the hall. The mosaics on show were discovered at the Corredera Square (Plaza de la Corredera) towards the end of the 1950s and formed part of the Roman Circus, as well as a sarcophagus from the 3rd Century. The hall is currently a highly sought after civil marriage location by many Cordoban citizens. Beneath the current floor of the hall, it is still possible to discover the remains of which are believed to be from the Royal Baths which were used by high dignitaries during the Muslim era.