It's important to understand that Columbus never realized he had discovered a new continent. He believed he had reached the East Indies, a group of islands in Asia, by sailing west.

It took several years and explorations by other European explorers to gradually realize that the land Columbus had reached was not part of Asia, but rather a new continent, which we now call the Americas.

Here's a breakdown of who contributed to this understanding:

* Amerigo Vespucci: He was a Florentine explorer who traveled to the New World in 1501 and 1502. He documented his voyages and accurately described the new landmass as a continent distinct from Asia. It's his name that eventually inspired the name "America."

* Ferdinand Magellan: He led the first expedition to circumnavigate the globe from 1519 to 1522. This journey solidified the understanding that the New World was a separate continent.

* Other explorers and cartographers: Various European explorers, such as Vasco da Gama, John Cabot, and others, continued to explore the New World, adding to the growing body of knowledge about its size and geography.

In summary, while Columbus initially believed he had reached the East Indies, it was through the contributions of other explorers and cartographers, like Amerigo Vespucci and Ferdinand Magellan, that the realization of a new continent emerged.