In 1492, the Catholic Monarchs of Castile and Aragon funded Christopher Columbus's plan to sail west to reach the Indies by crossing the Atlantic. Columbus discovered a continent uncharted by most Europeans (though it had begun to be explored and was temporarily colonized by the Norse some 500 years earlier). Later, it was called America after the explorer Amerigo Vespucci, who realized that it was a "new world". To prevent conflict between Portugal and Castile (the crown under which Columbus made the voyage), four papal bulls were issued to divide the world into two regions of exploration, where each kingdom had exclusive rights to claim newly discovered lands. These were modified by the Treaty of Tordesillas, ratified by Pope Julius II.