It was in his fourth voyage (1502) that Columbus first reached and explored the coastline of the isthmus and Central America. He was apparently not the first to land on the isthmus. That distinction belongs either to Alfonso Ojeda, who is said to have reached "Terra Firma" earlier in 1502, or to Rodrigo de Bastidas, who, we are told, set sail from Cadiz with La Cosa in 1500, and, reached the isthmus somewhere near Porto Bello. About the doings of Columbus on the mainland we get some detailed information from the Portuguese historian and explorer of the sixteenth century, Galvano. It is interesting to read that the great navigator visited the exact spot where the newly-constructed canal starts from the Caribbean coast. From the Rio Grande, we read, Columbus "went to the River of Crocodiles which is now called Rio de Chagres, which hath its springs near the South Sea, within four leagues of Panama, and runneth into the North Sea." It was this same river, as we shall see, that became the feeder of the canal when the high-level scheme was adopted. So far out of his reckoning was Columbus that at Panama he imagined himself to be ten days' journey from the mouth of the Ganges! One of his objects, as we know from his own journal, was to convert the Great Khan of Tartary to the Christian faith, and this entanglement in what he called "the islands of the Indian Sea" was a sore hindrance to that and all his other purposes. He began that search for the strait which engaged the attention and tried the temper of Spanish, Portuguese, and English navigators for the next thirty years. He had heard from the natives of the coast of "a narrow place between two seas." They probably meant a narrow strip of land as at Panama. But Columbus understood them to mean a narrow waterway, and rumours of such a passage no doubt existed then, as they still do among the isthmian tribes. He must also have heard accounts of the great ocean only thirty miles away, and it is rather surprising he should not have made a dash across and anticipated Balboa and Drake. In May 1503, however, he quitted the "Terra Firma" without solving the great secret, and he never returned to the mainland. He died in 1506, still in complete ignorance of the nature of his discovery. He knew nothing of the continent of America or of that seventy million square miles of ocean beyond, to which Magellan gave the name of "Pacific."