After regaining the city, the Spanish transformed Havana into the most heavily fortified city in the Americas. Construction began on what was to become the Fortress of San Carlos de la Cabaña, the third biggest Spanish fortification in the New World after Castillo San Cristóbal (the biggest) and Castillo San Felipe del Morro both in San Juan, Puerto Rico. On January 15, 1796, the remains of Christopher Columbus were transported to the island from Santo Domingo. They rested here until 1898, when they were transferred to Seville's Cathedral, after Spain's loss of Cuba.