To him it was but a part of Asia.

And as the main purpose of this fourth voyage was to find a way to sail straight to India--which he supposed lay somewhere to the south--he set off on his search.

The Indians told him of "a narrow place" that he could find by sailing farther south, and of a "great water." beyond it.

This "narrow place" was the Isthmus of Panama, and the "great water" beyond it was, of course, the Pacific Ocean.

But Columbus thought that by a "narrow place" they meant a strait instead of an isthmus.