Prince Henry the Navigator ascended to the position of Duke of Viseu due to his achievements in the conquest of Ceuta. It is said that he heard the legend of Prester John in Ceuta. Prester John is believed to be the king of a legendary Christian nation that exists in the East or Africa.
There were people in the Christian nations, which were continuously overwhelmed by Islamic forces, who believed that they could pincer the Islamic forces by cooperating with the nation of Prester John. The idea of a Christian nation in the East may seem absurd, but it is not entirely baseless. The Nestorian Christianity, which was deemed heretical at the Council of Ephesus in 431, had spread to Egypt, Persia, and even China. Previously, there were people who considered the Mongol Empire as the nation of Prester John. In reality, the Mongol Empire was neither a Christian nation nor an ally to the European nations.
Furthermore, Prince Henry the Navigator witnessed the trade of Islamic merchants. The spices obtained from the Moluccas had become incredibly expensive due to passing through the hands of Islamic merchants. The price of spices in Europe reached 360 times the cost price in the Moluccas. To obtain spices cheaply, it was necessary to buy them directly in Asia without going through Muslim intermediaries.
The legend of Prester John and spices. These became the driving force to develop a route that would circumnavigate the African continent and reach Asia.
Around 1416, Prince Henry the Navigator established a village at Cape St. Vincent, the southwesternmost point of Portugal, to advance the development of sea routes. He set up shipyards and schools for learning navigation. This is known as the "Prince's Village". The knowledge accumulated in the Prince's Village greatly contributed to the development of maps and navigation techniques.