Christopher Columbus believed he had reached Asia because of several key misconceptions prevalent at the time. Most importantly, he underestimated the size of the Earth, believing it to be smaller than it actually is. Based on this underestimation and the maps he had, he believed the distance across the Atlantic to Asia was much shorter—about 2,400 nautical miles—while the actual distance to Asia was roughly 10,600 nautical miles. This led him to conclude that the lands he encountered in the Caribbean were parts of Asia, like the East Indies or islands near Japan. Additionally, Columbus overestimated the size of Asia itself, believing Asia extended much further east than it does, which made it plausible in his mind that he had reached the outskirts of Asia after traveling a shorter distance. The knowledge of geography and the circumference of the Earth was still uncertain and debated at the time, so Columbus's calculations, influenced by sources like Paolo dal Pozzo Toscanelli, led him astray. He also based his belief on observations such as encountering peoples and environments he mistaken for Asian, and he was motivated and supported by Spanish monarchs eager for a western route to Asia. Columbus died believing he had found a new route to Asia, even though he had actually stumbled upon previously unknown continents.